UNIVERSITY  OF  CALIFORNIA   PUBLICATIONS 

IN 

AGRICULTURAL    SCIENCES 

Vol.  1,  No.  8,  pp.  173-274  August  25,  1914 


HUMUS    AND    HUMUS-NITROGEN    IN 
CALIFORNIA  SOIL  COLUMNS 

BY 

R.  H.  LOUGHRIDGE 


CONTENTS  „.„„ 

PAGE 
Introduction:  character  of  humus,  amount  produced  from  various  sub- 
stances; distribution  in  surface  soil  174 

Humus  in  California  Soils:  percentages  in  the  surface  foot  acording  to 

agricultural  regions,  by  quick  and  regular  analyses  176 

Distribution  of  Humus  downward  in  California  Soils:  bacterial  activity 

in  the  lower  depths  of  soil  columns  179 

Distribution  of  Humus  and  Humus-nitrogen  in  soil  columns  from  each 

agricultural  region  of  the  state  180 

Sacramento  Valley:  eighteen  soil  columns;  tables  of  analyses 181 

Alluvial  lands,  four  localities;  clay  loams,  seven  localities 181 

Black  adobe  soils,  four  localities;  Red  mesa,  three  localities 186 

Comparison  of  classes  or  types  190 

San  Joaquin  Valley:  twenty-four  soil  columns;  tables  of  analyses.  191 

Sandy  loams  and  clay  loam  lands,  ten  localities  192 

Gray  alkali  lands,  four  localities  196 

Black  clays,  loam,  and  reddish  clays,  eight  localities 197 

Delta  plains  of  Kings  and  Kern  rivers,  three  localities  201 

River  alluvial  lands  and  Tule  marshes,  two  localities  203 

Comparison  of  soils  of  different  types  204 

Lower  Foothills  of  Sierra  Nevada:  three  soil  columns;  analyses 208 

Coast  Range  Valleys:  twenty-four  soil  columns;  tables  of  analyses.  209 
North  of  Bay  Region:  Russian  River,  Santa  Rosa,  Los  Guillocos, 

Sonoma,  Napa,  and  Vaca  valleys  210 

The  Bay  Region:   Alameda  Plains,  Ignacio,   San   Ramon,   and 

Livermore   valleys   214 

South  of  the  Bay  Region:  Santa  Clara,  Pajaro,  Salinas,  Arroyo 

Grande,  Santa  Maria,  and  Lompoc  valleys  217 

Summary  of  results  for  Coast  Range  223 

Southern  California  Region:  twenty-six  soil  columns;   analyses 225 

Saticoy  Plain,   Santa  Clara   River  delta,  Pleasant   Valley  hill 

slope,  San  Fernando  and  San  Gabriel  valleys  226 

San  Bernardino  plains,  lowlands  and  mesas;  Los  Angeles  plain.  230 
Interior   Valleys:    Fallbrook   mesa,   Perris,   Escondido,   and    El 

Cajon  valleys  238 

Summary  for  Southern  California  columns  240 

Northeastern  Lava-bed  Region:  seven  columns;  tables  of  analyses.  241 
Honey  Lake  Valley;  East  Honey  Lake  Valley,  Madaline  Plains, 
Pitt  River  Valley,  Klamath  Lake  marshes,  Surprise  Valley....  241 


174  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

PAGE 

Soil  Columns  of  " Desert"  Plains:  four  soil  columns;  analyses 247 

Imperial    Valley,    Mojave   Mesa,    Coachella    and    Owens    Kiver 

valleys 247 

General  Summary  250 

Individual  soil  columns  having  the  highest  humus  content  250 

Columns  with  1  per  cent  in  each  of  upper  three  or  more  feet....  250 
Columns  having  the  highest  humus  percentages  in  first,  upper 

three  feet,  and  in  entire  column  respectively  251 

Composite  columns  of  agricultural  regions  252 

Nitrogen  in  the  humus  and  in  the  soil  258 

Humus  in  soils  of  different  texture;  in  columns  of  black  adobe  clay.  262 
Eelation   of  humus   percentages   to   color   and   other  soil   char- 
acters, texture,  color,  and  alkali  265 

Humus  phosphoric  acid  in  soils;  analysis  of  humus  ash  268 

Comparison  of  arid  and  humid  soils  270 

Conclusions  272 

INTRODUCTION 

Humus,  as  distinct  from  the  unhumified  organic  matter,  is 
now  regarded  as  one  of  the  most  valuable  ingredients  of  fertile 
soils  because  of  its  physical  effect  and  because  of  its  content  of 
nitrogen,  potash,  and  phosphoric  acid,  which  while  not  soluble  in 
water,  are  rendered  available  to  plant  use  by  the  action  of  soil 
bacteria.  It  has  no  definite  chemical  composition,  for  it  is  pro- 
duced by  the  decay  of  vegetable  and  animal  matters  of  all  kinds 
in  the  soil  and  under  certain  conditions  of  warmth  and  moisture, 
and  is  naturally  made  up  of  the  elements  found  in  those  sub- 
stances; during  the  process  of  humification,  however,  there  is  a 
gain  in  the  percentage  of  carbon  and  nitrogen  because  of  corre- 
sponding losses  of  oxygen  and  hydrogen.  The  proportion  of  these 
and  of  mineral  matters  in  the  humus  varies  then  with  the  nature 
of  the  substances  from  which  they  are  derived,  and  probably 
with  the  degree  of  intensity  of  the  action  of  each  factor  in  the 
humification  process,  in  which  oxidation  because  of  too  great  heat, 
or  other  changes  because  of  excess  of  water  may  be  brought  about. 

The  amount  of  humus  produced  from  organic  matter  depends 
upon  the  nature  and  condition  of  the  materials  used,  and  upon 
its  complete  humification  by  the  maintenance  of  proper  condi- 
tions in  the  soil.  Professor  Ililgard1  thinks  that  "in  the  humid 
region  one  part  of  normal  soil  humus  might  be  formed  from  five 
or  six  parts  of  dry  plant  debris;  while  in  the  extreme  regime 
of  the  arid   regions  from  eighteen  to  twenty  parts  of  the  same 


'  Soils  (Macmillan  &  Co.,  1906),  p.  128. 


1914]       Loughridge :  Humus  and  Nitrogen  in  California  Soil  Columns  1 75 

would  be  required."  The  experiments  of  Professor  Harry 
Snyder  of  Minnesota2  on  the  humification  of  different  materials 
gave  interesting  results.  Humification  under  favorable  condi- 
tions was  allowed  to  proceed  a  year  in  each  case,  at  the  end  of 
which  time  the  amount  of  humus  obtained  from  each  substance 
and  its  composition  was  ascertained.  Oat  straw  and  sawdust 
seemed  unchanged  even  when  humification  was  allowed  to  con- 
tinue longer  than  a  year.  The  following  table  illustrates  some 
of  Snyder's  findings: 

Table  1. — Humus  Obtained  from  Different  Materials 

Fresh  cow  manure  33  parts  for  1  part  of  humus  6.16%  nitrogen  in  humus 

Green  clover  25  parts  for  1  part  of  humus  8.24%  nitrogen  in  humus 

Meat  scraps  11  parts  for  1  part  of  humus  10.96%  nitrogen  in  humus 

Sawdust    10  parts  for  1  part  of  humus  0.30%  nitrogen  in  humus 

Oat  straw  6  parts  for  1  part  of  humus  2.50%  nitrogen  in  humus 

With  ordinary  green-manure  crops  and  under  field  conditions  it 
will  probably  require  a  much  larger  amount  of  green  material 
to  produce  one  part  of  humus,  for  there  are  losses  from  the 
incomplete  turning-under  of  the  material  and  the  drying-out  of 
the  soil. 

It  would  naturally  be  supposed  that  as  humus  is  formed  by 
the  decay  of  roots,  leaves,  etc.,  it  would  be  found  only  where 
formed,  whereas  on  the  contrary,  we  find  it  quite  evenly  diffused 
through  the  surface  soil;  this  even  distribution  is  not  easily 
accounted  for  without  some  outside  agencies.  Professor  Hilgard, 
in  discussing  the  subject,3  attributes  it  chiefly  to  the  action  of 
fungi,  insects,  and  earthworms. 

The  vegetative  fibrils  (mycelia)  of  several  kinds  of  molds  are  constantly 
present  in  the  soil,  and  while  consuming  dead  tissue  of  the  higher  plants, 
spread  their  own  substance  throughout  the  soil  mass.  .  .  .  All  these  being 
dependent  upon  the  presence  of  air  for  their  life  functions,  remain  within 
such  distance  from  the  surface  as  will  afford  adequate  aeration ;  the  depth 
reached  depending  upon  the  perviousness  of  the  soil  and  subsoil.  In  the 
humid  region  this  will  usually  be  within  a  foot  of  the  surface,  but  in  the 
arid  may  reach  to  several  feet.  .  .  .  The  earthworm  nourishes  itself  by 
swallowing,  successively,  portions  of  the  surrounding  earth,  digesting  a 
part  of  its  organic  matter,  and  ejecting  the  undigested  earth  in  the  form 
of  "casts"  such  as  may  be  seen  by  thousands  on  the  surface  of  the 


2  Bulletin  53  Minn.  Agr.  Exp.  Station. 

3  Soils  (Macmillan  &  Co.,  1906),  p.  157. 


176  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

ground  during  and  after  a  rain.  ...  In  humid  climates  and  in  a  ground 
fairly  stocked  with  these  worms  the  soil  thus  brought  up  may  amount  to 
from  one-tenth  to  two-tenths  of  an  inch  annually  over  the  entire  surface; 
so  that  in  half  a  century  the  entire  surface  foot  might  have  been  thus 
worked  over.  Aside  from  the  mechanical  effect  thus  achieved  in  loosen- 
ing the  soil,  and  the  access  of  air  and  water  permitted  by  their  burrows, 
the  chemical  effects  resulting  from  their  digestive  processes,  and  the  final 
return  of  their  own  substance  to  the  soil  mass;  also  their  habit  of  draw- 
ing after  themselves  into  their  burrows,  leafstalks,  blades  of  grass,  and 
other  vegetable  remains,  renders  their  work  of  no  mean  importance  both 
from  the  physical  and  chemical  point  of  view.  .  .  .  The  work  of  earth- 
worms is  especially  effective  in  loamy  soils  and  in  the  humid  regions. 
In  the  arid  region  and  in  sandy  soils  generally  the  life  conditions  are 
unfavorable  to  the  worm,  and  the  perviousness  elsewhere  brought  about 
by  its  labors  already  exists  naturally  in  most  cases. 

The  amount  and  nature  of  humus  depends  much  upon  climatic 
factors  as  is  especially  noted  in  arid  and  humid  regions.  In  the 
humid  region  with  its  frequent  rainfall  and  a  comparatively 
shallow  soil,  the  vegetable  material  (roots,  leaves,  etc.)  is  held 
near  the  surface  and  to  this  depth  the  humus  is  limited;  while 
in  the  very  deep  and  warm  soils  of  the  arid  region  the  penetration 
of  plant  roots  is  to  depths  of  fifteen  to  thirty  feet,  and  as  a 
consequence  of  their  decay  humus  is  found  to  depths  of  twelve 
or  fifteen  feet  and  in  some  cases  much  deeper. 

It  is  this  deep  distribution  of  humus  throughout  the  agricul- 
tural regions  of  California  that  is  treated  of  in  detail  in  this 
bulletin,  showing  a  fundamental  difference  between  the  soils  of 
humid  and  arid  regions. 


HUMUS  IN  CALIFORNIA  SOILS 

The  study  of  the  soils  of  California  was  begun  by  Professor 
Ililgard  immediately  after  entering  upon  his  duties  in  1874  as 
Professor  of  Agriculture  in  the  University  of  California,  and 
his  first  report,  made  in  1877,  contains  physical  and  chemical 
analyses  together  with  descriptions  of  a  number  of  soils,  as  well 
as  the  results  of  alkali  investigations.  The  analysis  of  a  soil  for 
its  humus  content  is  first  given  in  the  report  of  the  Experiment 
Station  for  1879,  and  since  then  nearly  every  annual  report  to 
and  inclusive  of  1904  contains  soil  descriptions  and  analyses,  the 
percentage  of  humus  being  given  for  the  first  foot  or  sometimes 


1914]       Loughridge:  Humus  and  Nitrogen  in  Calif omia  Soil  Columns         177 

for  the  upper  two  feet,  as  it  was  not  then  known  that  the  humus 
reached  to  a  greater  depth  than  three  feet.  In  the  report  for 
1904  the  first  analysis  is  given  of  a  soil  with  humus  to  a  depth 
of  twelve  feet. 

During  these  years  the  call  from  farmers  for  information 
regarding  the  needs  of  their  soils  was  very  great,  and  thousands 
of  soils  were  sent  in  for  examination.  These  did  not  require  an 
accurate  and  full  analysis  in  every  case,  and  were  subjected  to 
cursory  tests4  by  which  approximate  determinations  could  be 
reached  very  quickly  for  phosphoric  acid,  lime,  and  humus.  The 
results  were  graded  into  "poor"  for  less  than  0.7  per  cent; 
"fair"  for  0.7  to  1.0  per  cent;  and  "good"  when  the  percentage 
was  above  1.0,  and  only  the  surface  soils  were  examined.  From 
1893  to  1908  there  were  made  humus  tests  on  nearly  fifteen 
hundred  soils  distributed  among  the  following  agricultural 
regions;  in  this  table  are  given  the  percentages  of  soils  whose 
humus  belonged  to  the  several  grades. 

Table  2. — Humus  in  Soils  of  the  Agricultural  Regions;  Quick  Method 

No.  of  soils  Percentage  of  soils  having 

examined  Good  Fair  Poor 

Regions  for  humus  humus  humus  humus 

Sacramento  Valley  211  55  18  27 

San  Joaquin  Valley  434  24  24  52 

Foothills  of  Sierra  Nevada  66  59  12  29 

Coast  Range  valleys  398  64  19  17 

Southern  California  347  43  23  34 

Average    1,456  46  21  33 

It  will  be  seen  from  the  above  that  more  than  one-half  of  the 
soils  of  the  Sacramento,  Foothill,  and  Coast  Range  regions  that 
were  sent  for  examination  by  farmers  of  those  regions  had  as 
much  as  1  per  cent  of  humus,  though  for  the  state  at  large  only 
46  per  cent  of  the  1456  soils  had  that  amount. 

4  The  method  of  this  cursory  examination  for  humus  is  as  follows: 
Take  two  grams  of  air-dried,  well-mixed  soil  of  twelve  inches  depth,  place 
in  a  test-tube  of  one-half  inch  diameter  and  add  about  ten  cubic  centi- 
meters of  10  per  cent  solution  of  potassic  hydrate.  Boil  for  a  few  minutes 
and  allow  the  soil  to  settle.  The  potash  dissolves  the  humus  and  produces 
a  dark  color  of  greater  or  less  intensity  according  to  the  amount  of  humus 
present.  By  taking  soils  in  which  the  humus  percentages  have  already 
been  ascertained  correctly,  and  treating  them  by  this  short  method,  a 
scale  of  color  intensities  may  be  adopted  by  which  approximate  percent- 
age of  humus  may  be  reached  in  most  of  the  soils. 


178  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

The  results  of  these  soil  examinations  have  brought  out  the 
fact  that,  while  the  supply  of  potash  is  as  a  rule  very  large  and 
should  not  need  replenishment  by  fertilizers  for  decades  of  years 
and  that  phosphoric  acid  is  generally  fair  in  amount,  except  in 
lands  that  have  been  in  wheat  culture  for  many  years,  the  per- 
centage of  humus  in  all  surface  soils  except  tule  swamps  is  quite 
low  and  has  required  a  system  of  green  manuring  to  bring  the 
land  back  into  the  best  condition. 

Regular  Analyses. — Since  the  establishment  of  the  station, 
nearly  six  hundred  complete  analyses  have  been  made  of  soils 
chosen  to  represent  the  different  agricultural  regions  and  con- 
ditions in  the  state,  and  among  the  determinations  was  that  of 
the  exact  amount  of  humus  in  331  surface  soils.  The  method  of 
analysis  used  was  what  is  known  as  the  Grandeau  Method  as 
modified  by  Professor  Hilgard.  The  results,  therefore,  more 
nearly  represent  actual  average  conditions  in  the  soils  of  the 
state.  The  following  table  shows  the  average  percentages  of 
humus  in  the  soils  of  the  several  regions : 

Table  3. — Percentages  of  Humus  in  Surface  Soils;  Eegular  Method 

No.  of  soils  Average  Percentage  of  soils 

examined  for  percentage  having  more  than 

Regions                                                                humus  of  humus             1%  of  humus 

Tules  and  meadows  14  3.62                     all 

Coast  Eange  valleys  91  1.69  67 

Sierra  Foothills  46  1.23  41 

Sacramento  Valley  29  1.14  50 

Southern  California   61  .94  28 

San  Joaquin  Valley  67  .79  29 

Desert  plains  and  lava  bed  valleys  23  .51  0 

Genera]  average  for  state  331  1.25  40 


The  general  average  of  humus  in  the  331  surface  soils  taken 
from  different  parts  of  California  and  supposed  to  represent 
fairly  all  of  the  agricultural  regions  is  1.25  per  cent.  If,  how- 
ever, the  tule  marshes  and  the  meadow  lands  are  omitted  from 
the  calculation,  then  we  find  that  the  general  humus  percentage 
is  1.15. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         179 

DISTRIBUTION  OF  HUMUS  DOWNWARD   IN 
CALIFORNIA  SOILS 

A  very  marked  characteristic  of  the  soils  of  California  is  their 
great  depth,  as  exemplified  in  the  uniformity  of  color  through 
a  depth  of  several  feet,  their  good  texture,  affording  easy  pene- 
tration of  plant  roots  often  to  depths  of  twenty  and  even  sixty 
feet  below  the  surface,  abundant  food  available  for  plant  use 
throughout  these  depths,  an  absence  of  any  well-defined  subsoil 
except  at  a  depth  of  several  feet  below  the  surface,  the  absence 
of  any  compact  clay  substratum  differing  from  the  surface  foot, 
and  the  presence  of  humus  to  a  depth  of  as  much  as  ten  or  more 
feet.  In  each  of  these  particulars  the  soils  of  California  differ 
from  those  of  the  humid  states  east  of  the  Rocky  Mountains,  and 
because  of  this  the  methods  of  culture  are  different,  and  in  the 
applications  of  phosphate  fertilizers  to  the  soil  it  is  only  with 
great  difficulty  that  they  can  be  made  to  reach  the  feeding  roots 
of  plants. 

There  are  several  striking  facts  regarding  the  humus  itself 
in  the  soils  of  California  which  deserve  mention  and  which 
distinguish  them  from  the  soils  of  the  humid  region  of  the 
eastern  states,  one  of  which  has  but  recently  been  brought  out 
in  the  examinations  that  are  being  made  of  the  one  hundred  and 
more  typical  twelve-foot  columns  from  the  chief  agricultural 
divisions  of  the  state.  These  facts  are :  first,  the  small  percentage 
of  humus  in  the  first  foot  of  all  California  soils  as  compared 
with  the  much  higher  percentages  found  in  eastern  soils ;  second, 
the  distribution  of  the  humus  downward  to  depths  of  twelve  and 
more  feet  in  upland  soils,  the  total  amount  being  usually  greater 
than  that  of  the  eastern  soils;  and  thirdj  the  rather  higher 
percentage  of  humus-nitrogen  in  the  upper  three  feet,  and  the 
distribution  of  the  humus-nitrogen  throughout  the  twelve  feet. 
thus  giving  the  soil  in  the  arid  region  a  higher  total  of  humus- 
nitrogen  than  is  found  in  the  humid  soils. 

Bacterial  Activity  in  the  Soil. — Another  highly  important 
advantage  possessed  by  California  in  her  soils  is  the  fact  recently 
brought  out  by  Professor  C.  B.  Lipman  of  this  station  in  his 
paper,  "The  Distribution  and  Activities  of  Bacteria  in  Soils  of 
the  Arid  Region":5 


5  Univ.  Calif.  Publ.  Agr.  Sci.,  vol.  1,  no.  1,  pp.  17,  20. 


180  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

.  .  .  that  soils  of  the  arid  region  at  all  depths  studied  show  ammonifying 
powers,  which  are,  however,  generally  most  vigorous  in  the  first  six  or 
eight  feet.  In  one  case  ammonification  was  noted  in  soil  from  a  depth 
of  fifteen  feet,  or  adjoining  the  water-table.  .  .  .  As  for  nitrification  my 
data  present  again  features  of  striking  interest.  They  go  to  prove  that 
nitrate  formation,  like  ammonification,  goes  on  at  much  greater  depths 
in  soils  of  the  arid  than  in  soils  of  the  humid  region.  .  .  .  That  nitrifica- 
tion is  found  commonly  down  to  a  depth  of  five  or  six  feet  in  soils  of  the 
arid  region.  In  one  case  soil  from  an  eight-foot  depth  showed  a  vigorous 
nitrifying  power. 

Professor  Lipman's  observations  greatly  emphasize  the  im- 
portance of  having  the  roots  of  the  various  crops  utilize  the 
food-supplies  at  their  command  at  depths  of  many  feet;  for  not 
only  is  there  a  nitrogen  supply,  but  our  investigations  on  the 
soil  columns  show  that  the  amount  of  available  phosphoric  acid 
and  of  potash  is  large  at  depths  of  twelve  and  more  feet. 


DISTRIBUTION  OF  HUMUS  AND  HUMUS-NITROGEN  IN 

SOIL  COLUMNS  FROM  EACH  AGRICULTURAL 

REGION 

The  agricultural  regions  of  the  state  comprise  the  Sacramento 
and  San  Joaquin  valleys,  forming  together  the  central  Great 
Valley,  the  foothills  lying  on  the  western  slope  of  the  Sierra 
Nevada,  the  many  Coast  Range  valleys  and  low  hills  among  the 
mountain  ranges  along  the  western  side  of  the  state,  the  South- 
ern California  valleys  and  the  low  hills,  the  desert  plain,  which 
is  being  brought  under  cultivation  by  the  development  and  use 
of  irrigation  water,  and  the  northeastern  lava-bed  valleys. 

As  the  object  of  this  investigation  was  chiefly  to  ascertain  the 
extent  to  which  humus  was  found  in  the  lower  depths  of  the 
soils,  the  soil  columns  were  taken  only  from  those  regions  whose 
soils  are  many  feet  in  depth.  The  number  of  columns  obtained 
was  110  from  thirty-seven  counties,  each  column  intended  to 
represent  a  characteristic  type  of  land  in  its  particular  region. 
There  are,  of  course,  very  many  small  valleys  and  minor  soil 
regions  that  have  not  been  included  in  this  investigation.  The 
columns  have  been  placed  in  vertical  frames  against  the  walls 
of  the  lecture  room  of  Budd  Hall  at  the  University  of  California, 
arranged  and  labelled  according  to  the  respective  agricultural 
regions.      Each  soil    occupies    an    eight-ounce    bottle    and    the 


1914]       Loughridge:  Humus  and  Nitrogen  in  Calif 'omia  Soil  Columns         181 

columns  are  nearly  eight  feet  in  height,  thus  forming  a  very 
conspicuous  and  interesting  exhibit,  probably  the  first  and  only 
one  of  its  kind  anywhere. 

The  percentage  of  humus  and  of  humus-nitrogen  has  been 
ascertained  in  all  of  these  soils  as  shown  in  the  following  pages 
of  this  bulletin.  The  chemical  analysis  of  the  first,  sixth,  and 
lowest  foot  of  each  column  and  the  physical  analysis  of  the  first 
or  upper  foot  have  been  nearly  completed  and  the  results,  with 
proper  discussion,  will  be  given  in  future  bulletins.  The  humus 
and  nitrogen  determinations  in  the  bulletin  were  made  chiefly  by 
Messrs.  M.  E.  Holter  and  F.  H.  Wilson,  and  the  late  F.  E. 
Johnson,  assistants  in  the  soil  laboratory. 

SOIL  COLUMNS  OF  THE  SACRAMENTO  VALLEY 
The  valley  of  the  Sacramento  River,  lying  between  the  two 
great  mountain  ranges — the  Sierra  Nevada  on  the  east  and  the 
Coast  Range  on  the  west — which  unite  on  the  north,  covers  an 
area  of  6200  square  miles.  The  valley  is  widest  on  the  south, 
where  it  unites  with  the  San  Joaquin  Valley.  Within  its  area 
are  four  or  five  general  and  highly  distinct  soil  regions,  or  types, 
each  of  which  is  represented  by  one  or  more  soil  columns  in 
our  collection,  or  eighteen  in  all. 

Alluvial  Lands. — These  border  the  Sacramento  River  and  are 
timbered  with  sycamore,  white  oak,  and  ash.  The  soil  is  a  dark 
loam  with  little  or  no  change  to  the  depth  of  twelve  feet,  as  shown 
in  the  soil  columns,  and  even  deeper.  Three  columns  were  taken 
from  the  following  localities:  Near  Cottonwood,  Shasta  County, 
by  W.  S.  Guilford ;  Glenn  Post  Office,  in  Glenn  County,  east  of 
Willows;  and  near  Perkins,  Sacramento  County,  by  Professor 
George  Roberts,  now  of  the  Kentucky  Agricultural  College.  To 
these  is  added  a  column  of  the  alluvial  of  Chico  Creek  taken 
from  the  Bidwell  place,  at  Chico,  Butte  County. 

The  alluvial  lands,  with  the  exception  of  the  sample  from  the 
hop  fields  at  Perkins,  may  be  regarded  as  rich  in  humus  in  the 
upper  three  feet,  while  all  show  fair  amounts  below  that  depth. 
The  soil  texture  is  good  and  it  is  to  the  advantage  of  plant  roots 
that  the  humus  with  its  nitrogen  should  be  thus  distributed,  the 
sum  in  each  of  the  four  columns  being  from  5.60  to  8.80  per  cent. 


182  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


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1914]       Loughridge :  Humus  and  Nitrogen  in  California  Soil  Columns         183 

There  is  but  little  doubt  that  the  humus  in  both  the  Cotton- 
wood and  Chico  soils  reaches  much  deeper  than  the  twelve  feet 
in  which  the  percentage  is  quite  large,  for  the  soil  texture  is 
especially  favorable  for  deep  development  of  tree  and  plant  roots, 
from  the  decay  of  which  the  humus  was  doubtless  derived.  In 
the  Chico  column  there  is  a  sudden  increase  of  humus  in  the 
twelfth  foot  (0.52  per  cent),  which  would  indicate  former  strong 
development  of  roots  at  that  point,  probably  just  above  a  water 
stratum. 

The  humus  of  the  Cottonwood  column  is  richest  in  nitrogen 
in  the  upper  three  feet  and  shows  remarkable  and  a  sudden 
increased  percentage  in  the  tenth  foot. 

The  Chico  humus  is  interesting  because  of  its  richness  in 
nitrogen  in  the  lower  half  of  the  column. 

The  Cottonwood  and  Chico  columns  alone  of  the  four  have 
humus  in  sufficient  amount  and  richness  to  give  general  averages 
of  more  than  0.05  per  cent  of  nitrogen  in  the  entire  soil  column, 
and  are  the  only  ones  having  as  much  as  0.10  per  cent  of  nitrogen 
in  the  upper  three  feet  of  soil. 

Clay  Loams  of  the  Valley. — These  reach  south  from  near  Red 
Bluff  and  occupy  the  central  part  of  the  Sacramento  Valley.  As 
typical  of  this  class  of  soils,  seven  columns  were  obtained  from 
the  following  localities:  three  miles  west  of  Tehama,  Tehama 
County;  Willows,  Glenn  County;  J.  W.  Walton's  place  a  few 
miles  south  of  Yuba  City,  Sutter  County;  Woodland,  Yolo 
County;  the  University  Farm,  Davis,  Yolo  County;  Live  Oak, 
Sutter  County,  and  from  near  Elmira,  Solano  County.  In  each 
case  a  depth  of  twelve  feet  was  reached,  except  at  Live  Oak, 
where  at  nine  feet  the  presence  of  water  prevented  a  deeper 
sampling. 

The  clay  loams  of  the  Sacramento  Valley  are  generally 
deficient  in  humus,  as  shown  by  the  first  foot  in  each  of  these 
seven  typical  columns  and  by  the  results  of  previous  examination 
of  soils  from  many  localities,  the  average  being  below  1  per  cent. 
The  cause  is  chiefly  continuous  grain-growing  with  shallow 
cultivation  on  these  lands  for  thirty  or  forty  years,  which  has 
depleted  them.  This  is  prominently  shown  in  the  soil  from  the 
University  Farm  at  Davis  which,  before  purchase  by  the  Univer- 


184  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


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1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns  1H~j 


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186  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

sity,  had  been  in  grain  culture  for  thirty  or  more  years.  The 
humus  in  its  subsoil  is  nearly  double  that  of  the  soil  and  even  in 
the  fourth  foot  is  equal  to  that  of  the  soil  itself.  A  sample  of 
virgin  soil  taken  near  this  spot  was  found  to  have  1.25  per  cent 
of  humus,  which  was  probably  the  original  amount  in  the  field, 
thus  showing  a  loss  of  nearly  30  per  cent.  The  nitrogen  in  the 
virgin  soils  was  0.07  per  cent,  but  in  the  cultivated  was  but  0.04 
per  cent,  which  is  a  loss  of  more  than  40  per  cent  of  nitrogen. 

It  will  be  noted  that  the  percentage  of  humus  in  the  Davis  soil 
below  the  upper  foot  is  greater  throughout  its  twelve  feet  than 
in  any  other  of  the  columns.  This  may  be  accounted  for  by  the 
greater  development  of  the  root  systems  each  year  and  their 
subsequent  humification.  Investigation  made  by  Mr.  Farrer, 
formerly  of  the  University  Farm,  showed  that  the  roots  of 
wheat,  barley,  and  the  California  poppy,  coincident  with  those 
of  orchard  trees,  reached  water  at  a  depth  of  twelve  or  thirteen 
feet.  If,  as  is  probable,  this  had  been  the  case  for  many  years, 
the  amount  of  root  material  for  humification  has  been  large 
enough  for  these  results.  The  humus  nitrogen  of  the  surface 
foot  is  greatest  in  the  Woodland  and  Yuba  City  soils,  0.07  per 
cent  and  0.06  per  cent  respectively ;  but  those  columns  were  taken 
from  an  uncultivated  lot  near  Woodland  and  from  the  Walton 
orchard  south  of  Yuba  City. 

Previous  analyses  of  other  clay-loam  soils  gave  the  following 
percentages  of  humus  in  the  surface  foot:  Dixon,  1.71;  Kell's 
place  near  Yuba  City,  1.28,  and  north  of  Willows,  3.61. 

The  humus  in  these  columns  from  the  seven  localities  is  not 
especially  rich  in  nitrogen  with  the  exception  of  the  lower  por- 
tion of  that  from  Walton's  place  south  of  Yuba  City;  but  the 
amount  of  humus  is  so  small  that  the  nitrogen  given  to  the  soil 
is  very  little  in  amount.  The  soils  from  Walton's,  Woodland, 
and  Davis  are  the  only  ones  of  the  group  whose  upper  three  feet 
have  the  normal  of  0.05  per  cent  of  humus-nitrogen,  that  of 
Davis  being  0.08  per  cent,  or  approximately  9000  pounds  per 
acre. 

Black  Adobe  Clay  Soils. — There  are  several  regions  of  these 
black  clays  within  the  eastern,  western,  and  southern  parts  of 
the  Sacramento  Vallev.     One  of  these  reaches  from  southwest 


1914]       Loughridge:  Humus  and  Nitrogen  in  Calif 'ornia  Soil  Columns         187 


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188  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

of  Yuba  City  northward,  passing  west  of  Gridley  and  beyond 
Biggs.  A  column  was  taken  from  this  belt,  a  few  miles  south- 
west of  Yuba  City,  the  surface  soil  of  which  contained  39  per 
cent  of  clay.  Below  this  upper  foot  the  color  changed  from  black 
to  gray.  Another  column  was  taken  by  Mr.  F.  E.  Johnson  from 
near  Biggs.  This  contained  50  per  cent  of  clay  in  its  upper 
foot  and  the  black  color  changed  to  gray  below  the  third  foot. 

A  region  of  black  clay  lies  three  miles  east  of  Willows,  Glenn 
County,  whose  surface  foot  contains  47.46  per  cent  of  clay,  and 
the  black  color  extends  through  five  feet.  A  column  of  this  was 
taken  to  the  depth  of  twelve  feet. 

A  few  miles  south  of  Dixon,  Solano  County,  there  is  a  large 
body  of  very  black  adobe  clay  having  61.75  per  cent  of  clay, 
and  the  black  color  passes  through  three  feet,  changing  to  gray 
below.  This  soil  contains  the  highest  percentage  of  clay  thus 
far  found  in  any  black  adobe  in  the  state. 

The  black  adobe  clays,  with  the  exception  of  that  from  east  of 
Willows,  are  a  disappointment  with  respect  to  their  humus 
content,  for  we  had  anticipated  finding  fully  1.5  per  cent  in 
each  of  the  upper  three  or  four  feet,  or  hoped  that  they  would 
at  least  come  up  to  the  average  of  the  other  109  columns  of  the 
collection,  whose  summation  for  three  feet  is  2.81  per  cent.  It 
is  evident  from  the  results  that  a  black  color  does  not  always 
mean  a  high  percentage  of  humus,  for  the  densely  black  adobe 
of  Biggs  and  that  south  of  Dixon  each  had  less  than  the  much 
lighter  colored  soils  elsewhere,  and  less  than  one-half  that  of 
the  reddish  alluvial  soil  of  Chico  Creek.  The  samples  from  Biggs 
and  Yuba  City  are  from  the  same  belt  of  black  adobe,  though 
many  miles  apart,  and  each  shows  very  small  percentages  below 
the  first  foot.  Clearly,  these  clays  would  be  greatly  benefited  in 
texture  and  richness  by  a  good  system  of  green-manuring. 

The  humus  in  the  adobe  soils  from  the  several  localities  and 
even  in  the  respective  depths  of  each  column  is  not  uniformly 
rich  in  nitrogen,  as  will  be  seen  by  reference  to  the  table.  It  is 
sometimes  richest  at  a  depth  of  several  feet,  and  frequently 
there  is  a  sudden  and  great  diminution  in  an  adjoining  level, 
the  cause  of  which  is  not  apparent. 


1914]       Loughridge :  Humus  and  Nitrogen  in  California  Soil  Columns  1 89 

The  humus  of  the  adobe  soils  contains  on  an  average  about 
5.5  per  cent  of  nitrogen  in  the  first  foot  and  4.9  per  cent  in 
the  entire  column.  The  amount  in  the  top  soil  is  greatest  in  the 
Willows  adobe  (0.09  per  cent),  and  least  in  the  Biggs  soil  (0.03 
per  cent),  or  an  average  of  0.06  for  four  soils.  This  is  equivalent 
to  2400  pounds  of  organic  nitrogen  per  acre  in  the  surface  foot 
which,  under  the  proper  ammonifying  and  nitrifying  conditions, 
is  gradually  converted  into  an  available  supply  for  plant  use. 

The  humus  of  the  soil  near  Dixon  is  richest  in  nitrogen  both 
in  the  surface  foot  and  in  the  upper  three  feet,  though  the  amount 
of  humus  is  not  so  great  as  in  that  from  Willows. 

The  amount  of  humus  must  be  at  least  1  per  cent,  and  its 
nitrogen  content  must  be  fair  to  give  to  a  soil  the  0.05  per  cent 
which  is  regarded  as  sufficient  for  present  fertility,  and  we  find 
that  of  these  four  localities  the  soil  from  Biggs  falls  short  in  the 
first  foot  and  that  from  Yuba  City  in  the  second  and  third  foot 
respectively. 

The  percentage  in  the  soils  is  naturally  less  and  less  down- 
ward as  the  humus  diminishes,  and  there  are  but  traces  of 
nitrogen  in  the  lower  half  of  each  column.  The  natural  nitrogen 
supply  for  the  roots  of  crops  must  clearly  come  from  the  upper 
three  feet  in  each  locality,  that  from  Willows  being  equivalent 
to  about  8000  pounds  per  acre  in  three  feet  depth. 

Red  Mesa  and  "bedrock"  Lands. — These  form  a  wide  border 
along  the  eastern  and  northern  sides  of  the  valley,  reaching 
south  into  San  Joaquin  County,  and  are  characterized  by  usually 
shallow  soils  underlaid  by  either  heavy,  compact  red  clays  or  by 
cemented  beds  of  gravel  and  grit,  forming  a  hardpan  or  bedrock 
at  depths  of  from  two  to  five  feet  below  the  surface.  Because 
of  the  shallowness  of  these  lands,  this  region  is  represented  by 
but  three  columns;  one  from  the  bluff  of  Oat  Creek  southwest 
from  Red  Bluff,  and  one-half  mile  west  of  the  Corning  road ; 
another  from  near  Sheridan,  Placer  County,  representing  the 
lands  on  the  eastern  side  of  the  valley;  and  the  third  from  near 
Acampo  in  San  Joaquin  County,  taken  by  Mr.  P.  E.  Johnson. 

The  red  soils  from  Sheridan  and  from  the  mesa  southwest 
from  Red  Bluff  show  very  low  percentages  of  humus,  not  only 


190  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


Table 


-Humus  in  the  Soil  Columns  of  Eed  Mesa  Lands 


PLACER 

COUNTY 

TEHAMA    COUNTY 

SAN  JOAQUIN  COUNTY 

Sheridan 

South 

of  Red 

Bluff 

ACAMPO 

Soil 
Clav  15.52 
Ft,                           H 

umus 

Humus- 
Nitrogen  in 

Soil 
Clay  13.76 

Humus 

Humus- 
Nitrogen  in 

Soil 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

.Humus 

Soil 

Humus  Soil 

1   Red  loam  .... 

.40 

10.52 

.04 

Red  loam  . 

.42 

6.66 

.03 

Red  loam 60 

7.02      .04 

2   Red  loam  .... 

.38 

9.21 

.04 

Red  loam  . 

...       .28 

5.17 

.02 

Red  loam 18 

7.80      .01 

3   Red  clay  .... 

.13 

Red  loam  .. 

...       .22 

2.75 

.01 

Red  loam 10 

4   Red   clay   .... 

.10 

Red  loam  .. 

...       .08 

1.25 

Red  loam 10 

5   Light  red  clay 

.05 

Red  loam  .. 

..       .09 

Red  loam 10 

6   Light  red  clay 

tr. 

Red  loam  .. 

...       .10 

Red  loam 07 

7   Light  red  clay 

Red  loam  .. 

..       .07 

8    Light  red  clay 

Red  loam  .. 

..       .07 

9   Light  red  clay 

Red  loam  .. 

..       .09 

10  Yellow  clay.. 

Red  loam  .. 

..       .10 

Sum  of  per  cents 

L.06 

1.52 

1.15 

Average  per  foot 

.10 

.15 

.19 



Upper  3  feet  :* 

Sum  of  per  cents 

.91 

.92 

.88 

Average  per  foot 

.30 

9.85 

.04 

.31 

4.80 

.02 

.29 

*  Range  of  most  annual  plant  roots. 


in  the  first  foot  but  in  each  succeeding  level  down  to  the  tenth 
foot.  The  entire  amount  in  each  column  is  but  little  more  than 
the  average  of  the  first  foot  for  the  state  at  large.  The  darker 
clay  soil  from  the  region  of  Acampo  has  more  humus  in  the 
surface  foot  and  but  very  little  in  the  lower  depths. 

The  humus  of  the  Sheridan  and  Acampo  soils  is  rich  in 
nitrogen,  but  the  quantity  of  humus  itself  is  so  small  that  the 
amount  given  to  the  soil  is  very  little,  and  below  the  second  foot 
was  inappreciable. 

The  other  soil  is  peculiar  in  having  a  humus  that  contains 
very  little  nitrogen  in  its  third  and  fourth  foot.  As  a  consequence 
the  soil  itself  is  very  poor  in  nitrogen. 

All  of  these  soils  need  good  green-manuring  with  some 
nitrogen-rich  legumes  for  several  successive  years  to  improve 
their  texture  and  their  productiveness. 

Comparison  by  ('lasses. — The  average  percentages  of  humus 
in  composite  columns  of  soils  of  the  same  class  gives  an  indication 
of  wlial  to  expect  in  lands  of  these  four  classes. 


1914]      Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         191 


Table  8. — Averages  of  Humus  in  Soil  Types,  Sacramento  Valley 

Black  adobe  Stream  alluvial    Clay  loam    Red  mesa  and 

Composite  columns                                clay  loam  of  plains  bedrock 

4  columns  4  columns  7  columns  3  columns 

Humus  in  first  foot  1.16  1.47  .99  .47 

Sum  of,  in  upper  3  feet 2.41  3.54  2.40  .90 

Sum  of,   in  entire  column 3.88  7.50  4.91  1.25 

Nitrogen  in   humus — 

In  first  foot  5.56  5.51  4.68  8.58 

Average  in  upper  3  feet....       5.45  5.78  5.53  7.32 

Average  in   entire  column       4.96  6.46  5.03  6.29 

Nitrogen   in  soil — 

In  first  foot   06  .06  .05  .04 

Average  in  upper  3  feet 04  .07  .05  .02 

Average  in   entire  column          .02  .04  .02  .01 


The  figures  speak  for  themselves,  and  show  that  the  alluvial  lands 
of  the  streams  are  richest  in  humus  throughout  and  that  the  clay 
loams  of  the  plains  are  next,  while  the  black  clay,  in  spite  of  its 
color,  contains  less  humus  in  the  upper  three  feet  and  in  the 
entire  column  than  the  lighter  colored  plains  soil.  As  a  rule,  the 
alluvial  lands  do  not  need  green-manuring  crops,  but  the  others, 
and  especially  the  red  lands,  would  be  greatly  benefited  thereby. 

Nitrogen  i)i  Humus  and  Soil. — There  is  but  little  difference 
in  the  percentage  of  nitrogen  in  the  humus  of  the  upper  three 
feet  of  each  group,  except  that  in  the  red  soils  the  figures  are 
highest :  but  for  the  entire  column  the  alluvial  lands  stand  at 
the  head,  with  an  average  of  6.46  per  cent. 

For  the  soil  itself  the  nitrogen  is  greatest  in  the  stream 
alluvial,  the  average  in  the  upper  three  feet  being  0.07  per  cent, 
or  approximately  2800  pounds  per  acre-foot ;  this  is  but  little 
more  than  the  minimum  amount  (0.05  per  cent")  that  is  regarded 
as  essential  to  fertility.  Other  groups  contain  less  than  the 
alluvial  throughout. 

SOIL  COLUMNS  OF  TITE  SAN  JOAQUIN  VALLEY 
San  Joaquin  Valley,  with  an  area  of  eleven  thousand  square 

miles,  possesses  seven  or  more  large  and  distinct  soil  types  or 
regions,  each  of  which  is  represented  in  our  soil  collection. 

Twenty-four  localities  in  eight  counties  were  selected  from 
which  to  secure  columns  of  soil  as  nearly  typical  as  possible  of 
each  region,  and  fifteen  of  the  columns  were  taken  to  depths  of 


192  Un  iversity  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

ten  or  twelve  feet,  the  others  being  limited  in  depth  either  by 
hardpan,  coarse  gravel,  or  other  obstruction  which  prevented  the 
penetration  of  the  soil  auger ;  sometimes  the  water-table  at  depths 
of  less  than  ten  feet  produced  such  a  mushy  condition  in  the 
soil  as  to  prevent  its  being  removed  by  the  auger. 

Gray  Sandy  Loams  and  Sandy  Soils. — The  greater  part  of 
the  San  Joaquin  Valley  is  covered  with  a  grayish  sandy,  and 
sandy  loam,  soil,  usually  deep  and  highly  productive  under  irri- 
gation or  adequate  rainfall.  Some  of  them  are  highly  charged 
with  alkali  salts  in  small  areas,  but  these  salts  can  be  removed 
by  proper  means  of  irrigation  and  subdrainage.  Calcareous  and 
black  alkali  hardpans  are  also  found  occasionally,  whose  injurious 
effects  can  be  corrected  by  proper  treatment. 

From  these  lands  we  selected  seven  localities  in  five  counties 
from  which  to  secure  representative  soil  columns;  three  of  these 
contained  large  amounts  of  alkali  salts  and  are  given  a  separate 
discussion.  Each  of  the  other  columns  was  taken  to  a  depth  of 
eleven  or  twelve  feet,  from  the  following  localities :  two  miles 
north  of  Exeter;  three  miles  west  of  Tulare;  one  mile  west  of 
Modesto;  and  near  Livingston;  taken  by  Mr.  F.  J.  Randolph. 

The  soil  from  west  of  Tulare  has  a  little  more  than  1  per  cent 
in  the  surface,  and  2  per  cent  in  the  upper  three  feet,  but  the 
others  in  the  table  fall  far  below  that  percentage,  the  Modesto 
and  Livingston  soils  being  especially  poor.  Humus  is  found 
throughout  the  entire  column  from  three  of  the  localities,  and 
contains  fair  percentages  of  nitrogen;  but  the  actual  amount  in 
the  soil  itself  is  very  small,  except  in  the  upper  three  feet  of 
the  Tulare  column.  The  Livingston  soil  is  little  else  than  sand 
and  is  very  poor  in  both  humus  and  nitrogen. 

Gray  Clay-Loam  Lands. — The  lands  of  the  west  side  of  the 
San  Joaquin  Valley,  derived  from  the  rocks  of  the  Coast  Range 
find  deposited  from  streams  apparently  more  sluggish  than  came 
from  the  Sierras  on  the  east,  contain  more  clay  and  are  of  the 
clay-loam  type  of  soil.  They  are  more  compact  than  are  the 
sandy  soils,  and  should,  therefore,  contain  more  humus  than  the 
latter.  Three  localities  where  the  columns  were  obtained  are  on 
the  west  side  of  the  valley,  one  mile  south  of  Tracy,  five  miles 
southwesl  of  Los  Banos,  nod  one  mile  west  of  Mendota. 


1914]       Loughridge :  Humus  and  Nitrogen  in  California  Soil  Column*. 


193 


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194 


Un  iversity  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


Table  10  — 

-Humus 

IN  C 

OLUMNS  OF  G 

rRAY  Cl 

;AY  LOi 

LMS, 

SAN    JOAQUIN    COUNTY 

MERCED    COUNTY 

South 

of  Tracy 

Los 

Banos 

Soil 
Clay  17.03 
Ft. 

Humus 

Humus- 
Nitrogen  in 

Humus  Soil 

Soil 
Clay  15.02 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

1    Clay  loam 

1.35 

5.20 

.07 

Clay  loam 

.      .68 

8.64 

.06 

2   Clay  loam 

.99 

5.39 

.05 

Clay  loam 

.48 

9.33 

.05 

3   Clay  loam 

.83 

4.06 

.03 

Clay  loam 

.44 

3.82 

.02 

4  Clay  loam 

.59 

3.81 

.02 

Clay  loam 

.      .38 

4.05 

.02 

5   Clay  loam 

.41 

4.11 

.02 

Clay  loam 

.34 

4.94 

.02 

6  Clay  loam 

.25 

3.93 

.01 

Clay  loam 

.      .28 

3.00 

.01 

7   Clay  loam 

.16 

3.51 

.01 

Clay  loam 

.      .30 

5.60 

.02 

8   Clay  loam 

.08 

3.51 

tr 

Clay  loam 

.      .30 

9.34 

.03 

9   Clay  loam 

.10 

2.81 

tr. 

Clay  loam 

.      .24 

4.67 

.01 

10   Clay  loam 

.10 

2.81 

tr. 

Clay  loam 

.      .22 

5.09 

.01 

11   Clay  loam 

.10 

Clay  loam 

.22 

6.37 

.01 

12   Clay  loam 

.08 

.... 

Gravel   

Sum  of  per  cents 

5.04 

3.88 

Average  per  foot 

.42 

3.91 

.02 

.32 

5.90 

.02 

Upper  3  feet:* 

Sum  of  per  cents 

3.17 

1.60 

Average  per  foot 

1.06 

4.88 

.05 

.53 

7.26 

.04 

San  Joaquin  Valley 

FRESNO   COUNTY 

Near  Mendota 

Humus- 
Soil  Nitrogen  in 

Clay  24.91  , * , 

Humus    Humus  Soil 

Clay  loam 55  7.10  .04 

Clay  loam 42  6.19  .03 

Clay  loam 38  7.10  .03 

Clay  loam 22  7.27  .02 

Clay  loam 17  7.65  .01 

Clay  loam 12  6.66  .01 

Clay  loam 22  4.09  .02 

Clay  loam 25  2.40  .01 

Clay  loam 40  2.00  .01 

Clay  loam 30  10.33  .03 

Clay  loam 23  2.60  .01 

Clay  loam 19  3.15  .01 

3.45 
.29  5.55      .02 


1.35 
.45 


6.79      .03 


Range  of  most  annual  plant  roots. 


The  Tracy  soil  is  the  only  one  of  the  above  group  which  con- 
tains a  fair  amount  of  humus  in  the  first  foot  and  in  the  three 
upper  feet.  But  in  its  lower  depths  it  is  much  poorer  than 
either  that  from  Los  Banos  or  Mendota.  It  is  interesting  to  note 
the  distribution  downward  in  the  two  latter  columns,  which  in 
the  twelfth  foot  contain  one-third  of  what  is  in  the  first  foot. 
The  lower  six  feet  of  the  Los  Banos  column  contains  about  one- 
half  as  much  as  the  upper  six  feet,  while  in  the  Mendota  column 
the  upper  and  lower  half  are  nearly  equal  in  their  percentages. 
The  upper  half  of  each  column  is  much  richer  in  nitrogen  than 
the  lower,  as  is  the  case  with  all  California  soils;  but  there  are 
only  traces  in  the  lower  six  feet  of  the  Tracy  column.  Deep 
rooting  of  plants  is  thus  more  favored  in  the  Los  Banos  and 
Mendota  soils  and,  with  an  increased  supply  of  humus  in  the 
surface  and  abundant  water,  these  soils  should  prove  to  be  fully 
as  productive  as  that  from  Tracy. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns 


195 


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196  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Gray  Alkali  Land, — The  three  columns  of  gray  sandy  and 
sandy  loam  valley  soils,  and  the  dark  loam  of  Tulare  Lake  were 
found  to  contain  high  percentages  of  the  several  alkali  salts,  and, 
therefore,  may  be  put  in  a  class  by  themselves  for  consideration. 

The  ''white  ash"  soil,  so  called  because  of  its  fine,  light  ashy 
and  silty  nature,  was  taken  from  near  a  vineyard  in  Central 
Colony,  several  miles  southwest  of  Fresno,  and  is  the  representa- 
tive of  a  large  region  lying  on  the  north  side  of  Kings  River  and 
reaching  to  within  two  miles  of  Fresno  and  eastward  toward 
the  foothills  of  the  Sierras.  The  soils  are  rich  and  have  been 
largely  devoted  to  grape-growing.  The  water-table  was  reached 
at  a  depth  of  four  feet,  the  soil  assuming  a  white  color  and, 
below  the  sixth  foot,  losing  all  traces  of  humus. 

The  Tulare  column  was  obtained  from  the  old  experiment 
station  tract  in  a  spot  where  all  vegetation  had  been  killed  by 
the  alkali  salts. 

The  Tulare  Lake  column  was  taken  a  number  of  years  ago 
from  the  bed  of  the  lake,  which  had  long  been  dried-out  to  many 
feet  in  depth. 

The  column  from  Miramonte,  fifteen  miles  west  of  Wasco, 
represents  what  seems  to  be  a  belt  of  low  lands  or  what  was  once 
a  slough  connecting  the  Tulare  Lake  with  Buena  Vista  and  Kern 
lakes ;  in  this  belt  southward  the  alkali  of  the  lakes  had  accumu- 
lated to  great  depths.  The  alkali  consists  chiefly  of  the  sulfates 
and  chlorids  (glaubers  and  common  salt),  and  in  this  column  was 
distributed  at  the  rate  of  one-half  of  one  per  cent  per  foot,  giving 
a  total  approximating  233,000  pounds  for  the  twelve  feet  per 
acre.    No  vegetation  other  than  scattering  alkali  weeds  was  seen. 

Analysis  of  the  upper  four  feet  of  each  of  these  columns  gives 
the  following  percentages  of  alkali  salts  calculated  also  to  pounds 
per  acre. 

Table  12. — Alkali  Salts  in  the  Upper  Four  Feet  of  the  Columns 

Percentage  in  Soil  Pounds  per  acre;  approximate 


Car-  Car- 

Sulfates    bonates    Chlorids  Total  Sulfates  bonates  Chlorids  Total 

Tulare    03           .04          .02  .09  4,800  6,400  3,200  14,400 

Central  Colony...       .25          .09          .01  .35  40,000  14,400  1,600  56,000 

Miramonte  55          .02          .09  .66  88,000  3,200  14,400  105,600 

Tulare  Lake  bed         .13          .07          .07  .27  20,800  11,200  11,200  43,200 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         197 

The  Fresno  and  Tulare  soils  have  been  under  cultivation  for 
the  past  few  years  and  the  alkali  has  been  kept  below  the  surface  ; 
as  a  consequence,  root  growth  was  greater  and  its  decay  and 
humification  produced  more  humus  than  in  the  Miramonte  and 
Tulare  Lake  soils.    There  was  also  less  of  alkali  salts. 

The  percentage  of  humus  in  the  first  foot  of  each  of  the 
columns,  except  that  of  the  lake,  is  not  very  much  lower  than 
in  other  gray  soils  of  the  Tulare  plains.  It  is  distributed  through 
the  entire  column,  except  in  the  water-soaked  lower  part  of  the 
white-ash  lands,  and  the  total  amount  is  greater  than  in  some 
of  the  alkali-free  columns  of  the  valley. 

The  results,  then,  apparently  show  that  neither  carbonate, 
sulfate,  or  chlorid  of  soda  have  any  injurious  effect  on  humus 
itself,  but  that  they  do  so  retard  or  even  kill  the  growth  of 
surface  plants  and  root  systems  as  to  cut  off  the  supply  of 
humus-forming  material.  The  humus  in  the  Tulare  Lake  bed 
column  is  exceptionally  low  in  nitrogen  from  some  cause  not 
now  apparent,  and  in  all  of  the  soils  the  nitrogen  percentage 
falls  below  the  minimum  required  for  fertility. 

The  conclusion  is  plain,  then,  that  where  a  green-manure  crop 
can  be  grown  by  keeping  the  injurious  alkali  salts  below  a 
depth  of  three  or  more  feet  by  irrigation  its  conversion  to  humus 
under  favorable  condition  is  not  interfered  with. 

Black  Adobe  Clay  and  Loam  Lands. — A  large  area  of  black 
adobe  land  occupies  a  region  in  San  Joaquin  County  extending 
from  two  miles  north  of  Calaveras  River  south  to  French  Camp 
slough  and  from  the  tules  or  marshes  of  San  Joaquin  River  east- 
ward towrard  the  hills,  and  is  timbered  with  oaks.  The  character 
of  the  soil  is  shown  in  a  column  twelve  feet  in  depth  taken  two 
and  one-half  miles  southeast  of  Stockton. 

The  region  continues  southward  in  a  narrow  belt  along  the 
base  of  the  hills  into  Kern  County,  being  known  in  Tulare 
County  as  "dry  bog"  because  of  its  tendency  to  break  up  into 
small  fragments  when  dry.  It  is  here  underlaid  by  a  reddish 
clay  loam,  from  which  it  is  sometimes  separated  by  a  whitish 
calcareous  and  silicious  lime  and  magnesia  bed  of  varying  thick- 
ness. Two  columns  of  this  black  clay  adobe  were  secured  from 
near  Porterville;  one  is  from  the  Williams  orchard  with  a  depth 


198 


University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


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1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns  L99 

of  seven  feet;  the  other  which  appears  in  the  table  of  analyses 
is  from  the  Henderson  orchard  and  twelve  feet  in  depth. 

On  the  west  side  of  the  valley  another  narrow  black  adobe 
belt  reaches  along  the  base  of  the  hills  from  west  of  Tracy  into 
Merced  County  on  the  south.  It  is  represented  by  a  column  of 
ten  feet  taken  three  miles  west  of  Tracy. 

Still  another  belt  of  black  land,  not  so  clayey  as  the  others, 
though  containing  from  12  to  14  per  cent  of  clay,  lies  three  miles 
west  of  Tulare ;  a  column  was  taken  from  it. 

It  is  a  matter  of  much  surprise  that  these  clay  soils  with  their 
very  black  color  should  have  so  small  a  percentage  of  humus, 
the  maximum  of  which  is  but  1.2  per  cent,  found  in  the  soil 
from  Porterville.  We  would  naturally  anticipate  finding  fully 
10  per  cent,  and  yet  in  the  Tracy  soil  there  is  less  than  1  per 
cent.  It  is  evident  that  the  necessary  conditions  of  moisture 
and  warmth  for  the  humification  of  the  vegetable  material  are 
not  present  in  these  very  close,  compact  clays.  The  Porterville 
soil  is  subjected  to  irrigation  several  times  annually,  while  that 
from  Tracy  is  not,  and  this  may  account  for  the  larger  amount 
of  humus  in  the  former.  In  the  Stockton  column  the  humus  is 
found  to  the  full  depth  of  twelve  feet,  while  in  the  others  it  was 
found  only  in  the  upper  six  feet. 

The  nitrogen  content  of  the  Stockton  soil  is  good  in  the  upper 
foot  and  fair  for  the  three  feet,  the  humus  itself  being  rich  in 
nitrogen,  but  in  the  other  columns  it  is  quite  low  and  suggests 
the  need  of  an  additional  nitrogen  supply,  either  through  green- 
manuring  or  artificial  fertilization. 

Reddish  Clay  Lands. — A  prominent  and  wide  region  of  lands 
of  this  character  occupies  a  large  part  of  the  eastern  side  of  the 
valley :  it  is  narrow  on  the  north  in  San  Joaquin,  Stanislaus. 
Merced,  and  Madera  counties,  and  on  the  south  in  Tulare  and 
Kern,  but  quite  wide  in  Fresno  County.  It  is  the  southern  exten- 
sion of  the  belt  of  "bedrock"  lands  of  Sacramento  Valley.  It 
is  largely  characterized  by  a  rocky  hardpan  of  cemented  gravel 
and  grit,  with  thicknesses  of  an  inch  to  as  much  as  twelve  inches 
and  even  more,  occurring  at  depths  of  from  two  to  six  or  eight 
feet  below  the  surface.  When  it  occurs  near  the  surface  the 
hardpan  gives  rise  to  a  rolling  or  hogwallow  feature.     An  exeel- 


200 


University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


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1914]       Loughridge:  Humus  and  Nitrogen  in  Calif  or nia  Soil  Columns         201 

lent  soil  underlies  the  hardpan,  however,  and  when  the  latter  is 
broken  up  by  dynamite  good  results  in  tree  growth  are  usually 
obtained. 

Columns  of  this  land  were  obtained  from  the  Butler  vineyard 
a  few  miles  east  of  Fresno;  from  the  Kearney  Park  west  of 
Fresno ;  from  Lindsay  in  Tulare  County ;  and  from  the  place  of 
H.  Mueller  two  miles  southwest  of  Farmington,  San  Joaquin 
County.  The  latter  perhaps  more  properly  belongs  to  the  adobe 
group,  though  lighter  in  color. 

These  lands  differ  somewhat  in  their  content  of  clay,  that 
from  Farmington  being  of  a  clay  nature  and  the  other  sanely 
loams.  The  soil  from  Farmington  contains  good  humus  per- 
centages in  the  three  upper  feet  and  throughout  the  entire 
column  of  ten  feet,  but  each  of  the  other  localities  shows  a 
deficiency  in  the  surface  foot,  and  throughout  the  entire  depths. 
In  the  soil  from  east  of  Fresno  a  hardpan  layer  was  struck  in 
the  sixth  foot,  but  was  broken  up  and  the  soil  below  it  was 
obtained;  no  humus  was  found  below  the  hardpan. 

The  high  humus  of  the  upper  three  feet  of  the  Farmington 
column  and  its  high  nitrogen  content  gives  to  the  soil  an  excellent 
nitrogen  percentage  of  0.12  per  cent,  or  approximately  14,000 
pounds  of  organic  nitrogen  per  acre  within  the  range  of  most 
plant  roots.  Bacterial  activity  in  this  soil  will  do  much  to  pro- 
mote an  abundant  nitrogen  supply  for  plants  and  consequent 
high  fertility.  The  humus  of  the  Kearney  Park  soil  is  rich  in 
nitrogen  throughout,  but  the  small  amount  of  humus  in  each  foot 
from  the  surface  down  gives  but  a  small  amount  to  the  soil,  the 
average  for  each  foot  being  0.03  per  cent,  or  about  1200  pounds 
per  acre.  The  other  soil  columns  are  also  low  in  their  nitrogen 
content. 

Delta  Plains  of  Kings  and  Kern  Rivers. — There  are  two  tracts 
of  this  class  of  lowlands  which  are  made  of  fine  sediment  brought 
down  from  the  Sierra  Nevada,  the  Coast  Range  on  the  west  con- 
tributing little  or  nothing  to  these  deltas  as  its  streams  mainly 
discharge  their  sediments  westward  to  the  Pacific. 

The  Mussel  Slough  region  bordering  the  Tulare  Lake  receives 
its  sediment  from  the  Kings,  Kaweah,  and  Tule  rivers,  and 
covers  a  very  large  area.    It  is  timbered  with  oaks,  and  the  nature 


202 


University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


of  its  soils  are  shown  in  columns  twelve  feet  deep  taken  respec- 
tively from  near  Corcoran  and  Armona  by  Mr.  F.  E.  Johnson. 

The  Kern  River  delta  farther  south,  with  an  area  of  about 
290  square  miles,  is  also  timbered  with  oaks.  It  is  represented 
in  the  soil  collection  by  a  column  taken  three  miles  southwest  of 
Bakersneld.    Water  was  reached  in  the  seventh  foot. 


Table  15.- 

— HCJMUS   IN 

Columns  of 

Delta  Lands,  San  Joaquin 

Valley 

Kings 

i  River  Delta 

Kern  River  Delta 

KIXGS 

COUNTY 

KINGS 

COUNTY 

"* 

KERN 

COUNTY 

A 

Armona 

Corcoran 

South  of 

1  Bakersfield 

Soil 
Clay  6.42 
Ft.                           Humus 

Humus- 
Nitrogen  in 

Humus  Soil 

Soil 
Clay  15.11 

Humus 

Humus- 
Nitrogen  in 

Humus  Soil 

Soil 
Clay  11.28 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

1    Sandy  

.46 

6.66 

.03 

Dark  loam.... 

.51 

8.26 

.04 

Loam 

.   1.46 

4.23 

.06 

2    Sandy  

.32 

7.02 

.02 

Dark  loam.... 

.24 

7.02 

.02 

Loam 

.      .71 

6.72 

.05 

3   Sandy  

.22 

7.66 

.02 

Dark  loam.... 

.24 

8.19 

.02 

Loam 

.      .32 

6.87 

.02 

5   Sandy  

.16 

7.02 

.01 

Gray  loam.... 

.24 

9.36 

.02 

Loam 

.      .18 

6.11 

.01 

4   Sandy 

.20 

7.72 

.02 

Gray  loam.... 

.11 

7.66 

.01 

Loam 

..      .40 

5.50 

.02 

6   Reddish  loam 

.18 

6.24 

.01 

Gray  loam.... 

.05 

Loam 

.      .30 

4.66 

.01 

7  Reddish  loam 

.24 

7.02 

.02 

Gray  loam.... 

.06 

Loam 

.      .26 

4.23 

.01 

8   Reddish  loam 

.18 

6.24 

.01 

Gray  loam.... 

.05 

9   Reddish  loam 

.20 

7.02 

.02 

Gray  loam.... 

.06 

10   Reddish  loam 

.16 

7.02 

.01 

Gray  loam.... 

.06 

11   Reddish  loam 

.16 

7.02 

.01 

12    Reddish  loam 

.16 

7.02 

.01 

6.98      .02 


Sum  of  per  cents  2.64 
Average  per  foot       .22 

Upper  3  feet  .* 

Sum  of  per  cents  1.00 
Average  per  foot       .33  7.10      .02 

*  Range  of  most  annual  plant  roots. 


1.62 
.16 


8.10      .02 


7.82      .03 


3.63 
.52 


2.49 
.83 


5.48      .03 


5.90      .04 


It  was  anticipated  at  the  outset  that  the  delta  loams  of  the 
Tulare  Lake  and  Bakersneld  regions  would  be  rich  in  humus  in 
at  leasl  the  upper  feet,  because  of  their  surface  vegetation  of 
grasses  and  weeds  and  fallen  leaves.  But  humification  of  these 
lias  not  taken  place  thoroughly,  and  we  find  that  the  amount 
of  humus  in  the  upper  three  feet  is  not  so  large  as  in  the  sandy 
loam  soils  of  the  plains.  The  surface  soil  of  the  Kern  delta  is 
the    richesl    in    humus,    which    gives   to   the   soil    its    per   cent   of 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  8oil Columns 


203 


nitrogen,  but  in  the  three  upper  feet  of  each  of  the  columns  both 
humus  and  nitrogen  are  below  the  minimum  for  fertility. 

River  Alluvial  Lands  and  Tule  Marshes. — The  rivers  of  the 
San  Joaquin  Valley  are  usually  bordered  by  narrow  bottom 
lands,  the  Merced  and  Kings  rivers  being  exceptions  where  they 
enter  the  valley  plains.  A  column  of  eight  feet  depth  was  taken 
by  Mr.  F.  E.  Johnson  from  the  land  of  Kings  River  near  Kings 
River  Post  Office,  and  is  the  only  representative  of  such  lands 
from  this  valley.  The  surface  soils  of  other  streams  have,  how- 
ever, been  examined  from  time  to  time  and  their  humus  content 
ascertained. 

The  tule  marshes  cover  a  very  large  region  at  the  junction 
of  the  San  Joaquin  and  Sacramento  rivers  and  are  divided  up  into 
"islands"  by  many  sloughs.  The  soils  of  these  islands  is  shallow 
and  peaty  though  rich,  and  water  appears  at  but  a  few  feet  below 
the  surface.    There  are  localities,  however,  where  a  deep  soil  may 

Table  16. — Humus  in  Columns  of  Lowland  Soils,  San  Joaquin  Valley 


Eiver  Alluvial 

Tule  Mars 

H 

FRESNO 

COUNTY 

SAN  JOAQUIN   COUNTY 

Kings  River 

P.  0. 

Stockton 

Soil 
Clay  4.58 
Ft.                           Humus 

Humus- 
Nitrogen  in 

Soil 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

Humus 

Soil 

1    Sandy  

1.29 

4.25 

.06 

Black  loam  

14.10 

5.85 

.83 

2    Sandy  

.77 

4.38 

.03 

Black  loam  

19.45 

1.82 

.94 

3    Sandy  

.44 

4.47 

.02 

Very  black  loam 

16.50 

5.20 

.85 

4   Sandy  

.33 

3.83 

.01 

Very  black  loam 

13.00 

4.41 

.57 

5    Sandy 

.31 

3.62 

.01 

Lighter  loam  .... 

6.92 

4.94 

.34 

6    Sandy  

.17 

4.97 

.01 

Lighter  loam    ... 

2.96 

4.35 

.i:; 

7    Sandy  

.17 

4.13 

.01 

Lighter  loam  .... 

2.12 

5.80 

.12 

8   Sandy  

.19 

3.72 

.01 

Lighter  loam  .... 

4.28 

5.09 

.2 'J 

9 

Clay    

1.44 

10.14 

.15 

10 

Clay    

.36 

2.33 

.01 

11 

Clay    

.34 

■J.l  Mi 

.01 

12 

(May    

.28 

6.07 

.01 

Sum  of  per  cents 

3.67 

81.75 

Average  per  foot 

.30 

4.16 

0.2 

6.81 

5.10 

.35 

Upper  3  feet :  * 

Sum  of  per  cents 

2.50 

50.05 

Average  per  foot 

.83 

4.40 

.04 

16.68 

5.30 

.88 

Range  of  most  annual  plant  roots. 


204  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

be  found,  and  from  one  of  these  a  column  of  twelve  feet  was 
obtained  for  us  by  Mr.  W.  W.  Mackie,  then  of  the  United  States 
Bureau  of  Soils.  It  was  taken  from  a  few  miles  northwest  of 
Stockton  and  is  an  excellent  representative  of  these  lands. 

The  river  alluvial  is  not  especially  rich  in  either  humus  or 
organic  nitrogen,  though  one  would  suppose  from  its  alluvial 
character  that  the  amount  of  vegetable  material  in  it  would  be 
great. 

The  tule  or  swamp  lands  near  Stockton  have  to  a  large  extent 
been  reclaimed  by  dykes,  by  pumping  out  the  water,  and  by 
protection  from  overflow.  They  contain  a  very  large  percentage 
of  decayed  vegetable  matter  consisting  of  tule  roots,  etc.,  and 
this  has  been  quite  largely  humified,  as  shown  by  the  tables, 
especially  in  the  upper  four  feet.  Below  this  depth  the  amount 
suddenly  drops  from  13  per  cent  in  the  fourth  to  6.9  per  cent 
in  the  fifth  foot,  and  from  1.4  per  cent  in  the  ninth  to  0.36  per 
cent  in  the  tenth  foot.  No  other  tule  soil  in  the  state  that  has 
been  examined  contains  so  high  a  percentage  of  humus  and 
organic  nitrogen,  probably  because  of  extra  favorable  conditions 
of  warmth  and  moisture  and  excess  of  vegetable  matter  in  the 
Stockton  column.  This  large  amount  of  humus  produces  acid 
soils,  and  liming  is  necessary  to  render  them  neutral  and  pro- 
ductive. The  0.83  per  cent  of  humus  nitrogen  in  the  surface 
soil  is  very  great,  being  equivalent  to  an  average  of  25,000  pounds 
per  acre.  There  is  a  still  greater  percentage  in  the  second  foot 
as  well  as  in  the  third;  but  below  the  latter  it  falls  off  rapidly 
to  the  minimum  of  0.01  per  cent  in  the  tenth  foot. 

Comparison  of  San  Joaquin  Valley  Soils  of  Different  Types 

The  table  below  gives  in  a  concise  form  the  relative  percent- 
ages of  humus  and  nitrogen  in  the  eight  soil  types  of  the  San 
Joaquin  Valley,  and  from  it  we  can  make  comparisons  more 
easily  than  from  a  study  of  the  soil  columns  themselves.  The 
types  arc  placed  in  the  order  of  highest  to  lowest  composite 
averages  of  humus  in  the  first  foot,  and  there  is  almost  the  same 
succession  in  the  combined  upper  three  feet  and  Hie  entire  column 
respect  ively. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         205 

Table  17. — Percentages  of  Humus  and  Nitrogen  According  to  Soil  Types, 

San  Joaquin  Valley 

Tule  Stream  Black  Red  Delta  Valley  Alkali  Lake 

marsh  alluvial  clays  lands  lands  loams  lands  bed 

1  col.  1  col.  4  col.  4  col.  3  col.      7  col.  3  col.  1  col. 
Humus — 

Per  cent  in  first  foot 14.10  1.29  1.09  .95  .81  .75  .34  .18 

Sum  of,  in  upper  3  feet     50.05  2.50  2.32  2.15  1.49  1.68  .91  .42 

Sum  of,  in  entire  column  81.75  3.67  2.93  3.51  2.63  3.13  1.58  1.20 
Average  per  foot  in  upper 

3  feet  16.68  .83  .82  .72  .49  .56  .30  .14 

Average  per  foot  in  entire 

column    6.81  .30  .25  .32  .22  .27  .12  .10 

Nitrogen  in  Humus — 

Average  in   first   foot 5.85  4.25  5.46  5.52  6.38  6.56  7.09  3.33 

Average  in  upper  3  feet       5.30  4.40  6.09  6.72  6.93  6.09  5.30  1.68 

Average  in  entire  column       5.10  4.16  7.10  7.06  6.85  6.10  5.33  1.46 

Nitrogen  in  Soil — 

Average  in   first    foot 83  .06  .06  .06  .04  .05  .03  .01 

Average  in  upper  3  feet           .88  .04  .04  .05  .03  .04  .02  .01 

Average  in  entire  column          .35  .02  .03  .03  .02  .02  .01  .01 


There  are  large  differences  in  the  amount  of  humus  in  the 
several  groups,  as  is  to  be  expected  from  soils  of  such  extremely 
different  characters,  the  highest  percentage  being  in  the  Stockton 
tule  marshes  and  the  lowest  in  the  strong  alkali  lands  and  in  the 
Tulare  Lake  bed. 

The  surface  soils  of  the  valley  are  not  rich  in  humus  as  a  rule, 
and  this  is  well  shown  in  these  tables.  Even  the  black  clays  and 
loams,  which  because  of  their  color  would  be  supposed  to  contain 
high  percentages,  were  found  to  have  but  little  more  than  1  per 
cent,  and  in  some  instances  less  than  that.  Similarly  the  alluvial 
and  delta  soils  of  Kings  and  Kern  counties  are  very  low  in 
humus.  The  tule  marshes  in  the  region  of  Stockton  are  naturally 
rich,  because  of  the  great  amount  of  vegetable  matter  such  as 
roots  and  leaves  that  have  accumulated  in  them,  and  we  find  as 
much  as  14  per  cent  of  humus  in  the  first  foot  and  19  per  cent 
in  the  second. 

Humus  and  Nitrogen  in  the  First  Foot. — The  general  average 
of  humus  in  the  surface  soils  of  the  state  is  1.25  per  cent,  and  it 
thus  appears  that  the  soils  of  the  San  Joaquin  Valley  fall  much 
below  that.  In  but  eight  of  the  columns  (omitting  the  Stockton 
tule)   is  there  as  much  as  1  per  cent  in  the  surface  foot,  the 


206  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

highest  being  found  in  the  brownish  lands  of  Farmington,  and  the 
lowest  of  0.18  per  cent  in  the  soil  of  Tulare  Lake  bed.  The 
general  average  of  all  is  0.80  per  cent,  which  is  much  below  the 
requirements  for  good  texture  and  productiveness. 

The  humus  of  the  surface  foot  contains  for  the  most  part  a 
fair  percentage  of  nitrogen,  the  general  average  being  5.98  per 
cent,  but  there  are  several  soils  in  which  the  humus  is  very  poor, 
and  a  high  amount  of  such  humus  is  necessary  to  give  to  the  soil 
an  amount  adequate  for  fertility.  It  is  thought  that  a  fertile 
soil  should  not  have  less  than  0.05  per  cent  of  organic  or  humus 
nitrogen  in  the  surface  foot,  and  from  the  tables  it  is  seen  that 
because  of  the  small  amount  of  humus,  many  of  the  soils  have 
much  less  than  0.05  per  cent. 

The  soil  richest  in  nitrogen  in  the  above  group  is  that  from 
Farmington  which,  because  of  the  abundance  and  richness  of  its 
humus,  has  0.14  per  cent  of  nitrogen,  equivalent  to  more  than 
5000  pounds  per  acre-foot.  The  sandy  soils  of  the  sandy  and 
black  loam  plains  west  of  Tulare  and  the  black  clay  southeast 
of  Stockton  each  contains  from  3000  to  3500  pounds  of  humus 
nitrogen  per  acre-foot. 

The  humus  of  the  Stockton  tule  soil  contains  a  fair  amount 
of  nitrogen,  and  the  very  high  percentage  of  the  former  gives 
to  the  soil  the  enormous  amount  of  0.83  per  cent  of  nitrogen, 
or  approximately  32,000  pounds  of  humus  nitrogen  per  acre-foot. 
The  second  foot  is  even  richer. 

Humus  in  the  Upper  Three  Feet. — The  range  of  annual  plant 
roots  in  California  soils  is  in  the  upper  three  feet,  and  this 
may  be  considered  as  the  true  soil.  This  combination  of  three 
feet  more  than  doubles  the  amount  of  humus  and  its  nitrogen 
that  is  to  be  regarded  as  directly  influencing  fertility,  though 
the  average  per  foot  is  lessened.  The  distribution  through  the 
three  feet  is  of  greater  advantage  than  if  concentrated  in  the 
upper  foot,  for  the  roots  thus  secure  their  nitrogen  in  a  moister 
soil  and  away  from  the  heated  surface.  The  general  average 
summation  of  humus  in  this  depth  of  three  feet  for  all  of  the 
columns,  omitting  the  Stockton  tule,  is  1.78,  or  0.66  per  cent  per 
foot,  and  this  is  about  one-third  less  than  for  the  state  at  large. 
The  humus  is  however  fairly  rich  in  nitrogen   (6.22  per  cent) 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         207 

and  had  the  former  been  more  abundant  the  percentage  given  to 
the  soil  would  have  been  sufficient  for  needs  of  crops. 

Humus  and  Nitrogen  in  the  Entire  Column. — Humus  was 
found  to  occur  to  depths  of  ten  or  twelve  feet  in  but  thirteen  of 
the  columns.  In  the  brown  land  of  Farmington  and  the  alluvial 
soil  of  Kings  River  it  would  clearly  have  been  found  at  that  depth 
had  the  columns  been  taken  to  twelve  feet.  On  the  other  hand, 
in  five  of  the  ten-foot  or  twelve-foot  columns  humus  was  not 
found  in  the  lower  four  or  five  feet.  The  percentages  diminished 
downward  from  the  first  foot  in  all  cases,  in  some  instances  very 
sharply,  and  usually  added  but  little  to  the  combined  percentage 
of  the  upper  three  feet.  The  Farmington  column  with  its  7.76 
per  cent  of  humus  is  the  richest  group  (excepting  the  Stockton 
marshes),  followed  by  the  Tracy  loam  and  Tulare  plains  soils. 
Twelve  of  the  columns  have  higher  total  amounts  of  humus  than 
the  average  of  several  hundred  soils  of  the  humid  region,  and 
doubtless  the  total  amount  of  organic  nitrogen  in  these  soils  is 
also  greater  than  that  in  the  humid. 

The  humus  not  only  varies  in  its  percentage  of  nitrogen  in 
each  of  the  twenty-five  localities  from  which  the  soils  were  taken, 
but  also  in  the  several  depths  below  the  surface  in  each  column. 
It  is  poorest  in  the  Tulare  Lake  bed  and  richest  throughout  the 
column  from  Kearney  Park,  where  each  foot  except  the  first 
contains  more  than  10  per  cent.  It  is  only  occasionally  that 
among  other  columns  is  there  found  a  humus  having  as  much  as 
10  per  cent.  The  general  average  of  all  is  but  6.22  per  cent,  a 
figure  too  low  to  benefit  the  soil  greatly  except  where  the  humus 
content  is  above  1  per  cent. 

The  sandy  loams  of  the  plains  which  comprise  the  greater 
part  of  the  San  Joaquin  Valley  and  the  red  lands  of  the  eastern 
side  of  the  valley  are  but  slightly  different  in  their  general 
averages  of  humus,  the  latter,  because  of  the  high  percentages 
in  the  Farmington  clay,  having  slightly  more  throughout  its 
column.  The  surface  soils  are  clearly  in  need  of  green-manure 
crops  that  will  supplement  that  humus  already  present.  The 
soils  are  liable  to  form  surface  crusts  where  there  is  so  little 
humus  present,  and  require  special  care  and  treatment  to  prevent 
injury. 


208  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

The  humus  of  both  plains  and  the  red  lands  is  fairly 
rich  in  nitrogen;  but  the  amount  for  the  soil  itself  is  below  the 
normal  of  0.05  per  cent  minimum,  except  in  the  first  foot.  These 
lands  therefore  need  not  only  more  humus  but  a  humus  that  is 
very  rich  in  nitrogen.  A  leguminous  crop,  such  as  the  spring 
vetch,  should  alone  be  used  for  humification,  for  by  it  the  land 
secures  a  greater  amount  of  green  stuff,  a  far  greater  amount 
of  nitrogen  than  if  grass,  rye,  or  alfileria  were  used,  and  such 
nitrogen  is  derived  chiefly  from  the  atmosphere. 

SOIL  COLUMNS  OF  THE  LOWER  FOOTHILLS  OF  SIEERA  NEVADA 

The  lower  foothills  of  the  Sierra  Nevada  rising  from  the 
valley  plains  to  an  elevation  of  2500  feet  above  sea-level  forms 
an  important  fruit-bearing  region.  The  soils  derived  from  slate 
and  granite  are  often  shallow  on  the  hillsides  but  deep  in  the 
valleys. 

Table   18. — Humus  in   Soil  Columns   of   Foothills 


BUTTE 

COUNTY 

PLACER 

COUNTY 

AMADOR    COUNTY 

Palermo 

Newcastle 

Experiment  Station 

Jackson 

Soil 
Clay  17.80 
Ft.                           Humus 

Humus- 
Nitrogen  in 

Soil 
Clay  14.17 

Humus 

Humus- 
Nitrogen  in 

Soil 
Clay  16.43 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

Humus 

Soil 

Humus  Soil 

1   Red   clay 

.96 

5.85 

.06 

Reddish  loam 

1.35 

7.45 

.10 

Red  loam  .... 

1.07 

4.50      .05 

2  Red  clay 

.36 

3.05 

.01 

Reddish  loam 

1.24 

9.72 

.12 

Red  loam  .... 

.54 

5.20      .03 

3   Gravelly  clay 

.20 

3.00 

.01 

Reddish  loam 

1.18 

6.37 

.08 

Red  loam  .... 

.35 

3.61      .01 

4   Gravelly  clay 

.22 

3.64 

.01 

Reddish  loam 

.60 

12.50 

.08 

Red  loam  .... 

.35 

3.61      .01 

5   Lighter  clay.. 

.12 



.... 

Reddish  loam 

.16 

8.76 

.01 

Red  loam  .... 

.25 

3.37      .01 

6  Lighter  clay.. 

.10 



..... 

Gravelly  clay 

.18 

8.32 

.02 

Granitic  clay 

.14 

4.01      .01 

7   Lighter  clay.. 

.10 



.... 

Gravelly  clay 

.34 

7.95 

.03 

Granitic  clay 

.10 

4.21      .01 

8 

Gravelly  clay 

.26 

9.63 

.03 

Granitic  clay 

.06 

4.75      .01 

9 

Gravelly  clay 

.08 

.... 

10 

Gravelly  clay 

.12 

.... 

11 

Gravelly  clay 

.07 

12 

Gravelly  clay 

.06 

Sum  of  per  cents 

2.06 

5.64 

2.86 

Average  per  foot 

.29 

3.91 

.02 

.47 

8.84 

.06 

.36 

4.16      .02 

Upper  3  feet :  * 

Sum  of  per  cents 

1.52 

3.77 

1.96 

Average  per  foot 

.51 

3.97 

.02 

1.26 

7.80 

.10 

.65 

4.44      .03 

Range  of  most  annual  plant  roots. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         209 

Columns  of  the  red  slate  soil  were  taken  from  Palermo,  Butte 
County,  and  from  the  former  experiment  station  tract  near 
Jackson,  Amador  County;  also  from  a  bluff  near  Newcastle, 
Placer  County,  taken  by  Mr.  Paul  H.  Steude  of  Newcastle. 

The  red  clay  soils  of  Jackson  and  Palermo  are  quite  similar 
in  the  amount  of  humus  in  the  first  foot,  but  the  former  is  the 
richer  below  that.  The  clay  is  quite  close  and  compact,  and  this 
has  prevented  the  development  of  roots  to  the  extent  permitted 
by  the  looser  gravelly  granitic  soil  of  Newcastle,  in  which  there 
is  more  humus.  The  general  average  of  humus  in  the  first  foot 
is  1.12  per  cent;  that  of  thirty-one  soils  of  the  foothills  previously 
examined  is  1.05  per  cent,  although  it  is  found  to  be  higher  in 
the  valleys  farther  up  in  the  mountains,  in  the  regions  of 
Auburn,  Grass  Valley,  Nevada  City,  and  Placerville,  than  near 
the  Sacramento  Valley.  In  percentage  summation  the  general 
average  of  the  upper  three  feet  of  the  columns  is  .80  per  cent. 

The  humus  in  each  of  the  Palermo  and  Jackson  soils  is  very 
poor  in  nitrogen,  not  only  in  the  upper  three  feet  but  in  the 
entire  column ;  and  the  nitrogen  of  the  respective  soils  is  also 
below  the  normal.  On  the  other  hand,  the  humus  in  the  soil 
from  Newcastle  is  far  richer  in  nitrogen,  there  being  as  much 
as  8.8  per  cent  in  the  humus  of  each  foot  of  the  twelve-foot 
column.  The  soil  itself  contains  0.10  per  cent  in  the  upper  three 
feet,  which  is  much  above  the  normal,  and  is  equivalent  to  about 
4000  pounds  for  each  foot  in  depth  per  acre. 

SOIL   COLUMNS   OF   THE   COAST   RANGE   VALLEYS 

The  Coast  Kange  of  mountains,  reaching  from  tbe  Oregon 
state  line  south  to  the  Mexican  border,  has  but  few  agricultural 
possibilities  except  in  the  many  valleys  enclosed  between  the 
mountain  ridges.  The  country  north  of  Mendocino  County  is 
especially  rugged  and  the  valleys  are  few,  but  southward  there 
are  many  valleys  that  present  splendid  agricultural  attractions, 
and  we  have  endeavored  to  have  the  soils  of  the  largest  and  most 
important  ones  represented  in  the  columns  of  this  series.  Of 
course,  it  must  be  understood  that  in  each  valley  there  are  a 
number  of  soil  variations  and  gradations  from  the  hills  to  the 
lower  vallev  center,  and  that  the  column  has  been  selected  to 


210         University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

represent  the  best  and  most  extensive  of  these,  the  object  being 
to  ascertain  to  what  depth  and  in  what  percentage  the  humus 
reaches  under  favorable  conditions. 

Fifteen  valleys  in  nine  counties  north  of  the  Santa  Ynez 
Mountains  have  their  soils  represented  in  the  series  of  columns, 
and  in  the  accompanying  tables  are  arranged  in  order  of  occur- 
rence from  north  to  south. 

We  may  conveniently  follow  the  usual  subdivision  of  the 
Coast  Range  counties  and  arrange  the  table  into  the  counties 
north  of  San  Francisco  Bay,  embracing  seven  soil  columns;  the 
bay  region  itself,  embracing  the  country  east  and  west  of  the  bay 
as  far  south  as  San  Jose,  represented  by  eight  soil  columns ;  and 
the  counties  south  of  the  bay  as  far  as  Santa  Barbara,  represented 
by  nine  soil  columns. 


North  of  the  Bay  Region 

The  valleys  represented  in  this  section  of  the  Coast  Range 
are  Russian  River,  Santa  Rosa,  Los  Guillocos,  Sonoma,  Napa, 
and  Vaca :  there  are  other  important  though  much  smaller  ones 
east  and  west  of  these  and  in  the  counties  further  north,  from 
which  we  were  unable  to  secure  columns. 

Russian  River  Valley. — The  soil  columns  from  this  valley 
were  taken  from  the  alluvial  lands  of  the  hop  fields  belonging 
to  Mr.  T.  Boone  Miller,  six  miles  south  of  Healdsburg,  and 
from  the  red  hills  three  miles  southwest  of  Healdsburg,  Sonoma 
County. 

Santa  Rosa  Valley. — The  western  part  of  the  valley  has  a 
heavy  adobe  soil,  which  is  not  so  largely  in  cultivation  as  the 
more  loamy  land  of  the  eastern  and  middle  part.  A  column  of 
twelve  feet  depth  was  taken  from  the  creek  alluvial  on  the 
Vrooman  orchard  east  of  Santa  Rosa. 

Los  Guillocos  Valley. — This  valley  is  not  very  wide  nor  long, 
and  it  opens  northward  into  Santa  Rosa  Valley.  Its  soil  is  a 
reddish  loam  and  is  represented  by  a  column  taken  a  short  dis- 
tance southeast  of  Kenwood,  Sonoma  County. 

Sonoma  Valley. — The  valley  opens  southward  to  San  Fran- 
cisco Bay  and  is  largely  covered  by  marsh  lands,  but  the  northern 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns  211 

part  is  higher  and  comprises  better  lands.  A  black  adobe  clay 
seems  to  be  the  prevailing  soil  and  a  column  of  this  was  taken 
near  the  village  of  El  Verano. 

Xapa  Valley. — The  soil  is  chiefly  loamy  in  nature,  intersj. 
with  some  adobe  belts  on  either  side.     A  column  of  the  former 
was  obtained  near  Yountville,  Xapa  County,  to  a  depth  of  twelve 
feet. 

Vaca  Valley. — This  valley  is  situated  among  the  foothills  on 
the  west  side  of  the  Sacramento  Valley,  into  which  it  opens,  and 
is  noted  for  its  early  fruits.  The  soil  is  chiefly  a  reddish  loam, 
as  shown  in  the  column  obtained  southeast  of  Vaca vi lie. 

These  valleys  are  characterized  by  having  a  high  humus  per- 
centage in  the  upper  foot  and  also  in  the  four  feet  which  is  the 
usual  range  of  plant  roots.  The  soil  from  Yountville.  Xapa 
Valley,  is  the  richest  of  the  group,  and  contains  nearly  6  per  cent 
of  humus  in  the  upper  three  feet.  The  Kenwood  and  El  Verano 
soils  are  the  next  in  humus  content,  each  containing  more  than 
2  per  cent  in  the  first  foot  and  more  than  5  per  cent  in  the  upper 
three  feet,  the  range  of  most  plant  roots.  A  notable  feature  in 
four  of  the  columns — Russian  River.  Santa  Rosa.  El  Verano.  and 
Yountville — is  that  there  is  more  than  1  per  cent  in  each  of  the 
upper  four  feet ;  in  the  Santa  Rosa  column  that  percentage  is 
found  in  six  feet  and  almost  in  the  seventh  foot.  The  distribution 
of  humus  downward  through  the  entire  column  of  twelve  feet  is 
good,  the  average  for  the  Russian  River  alluvial  being  more  than 
1  per  cent  for  each  foot,  while  the  Santa  Rosa  and  Yountville 
averages  very  nearly  equal  it.  This  is  a  splendid  record  and 
places  these  soils  among  the  best  in  the  state. 

The  humus  of  the  Kenwood  soil  is  richer  in  nitrogen  than 
that  of  any  other  column,  the  average  being  10.61  per  cent  for 
the  seven  feet.  That  of  the  Santa  Rosa  has  an  average  of  -Vv7 
in  its  twelve  feet.  The  richness  of  the  Kenwood  soil  is  chiefly 
in  its  lower  fourth,  fifth,  and  sixth  feet.  The  humus  of  the 
El  Verano  adobe  is  for  some  reason  or  other  weaker  in  nitrogen 
than  any  other  (except  in  its  first  foot),  the  general  average 
being  but  2.67  per  cent  in  each  foot. 

The  most  important  consideration,  however,  is  the  amount  of 
humus  nitrogen  occurring  in  the  soil,  and  we  find  it  to  be  highest 


212  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  ] 


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1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         213 


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214  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

(0.13  per  cent)  in  the  surface  soil  of  Vacaville  and  Kenwood, 
with  the  equivalent  of  about  5000  pounds  per  acre-foot;  the 
general  average  of  all  surface  soils  being  0.10  per  cent,  or  4000 
pounds  per  acre-foot.  This  is  a  very  good  amount.  In  a  depth 
of  three  upper  feet,  comprising  the  range  of  chief  feeding  roots 
of  the  plant,  we  again  find  the  highest  percentage  to  be  in  the 
Kenwood  soil,  with  an  average  of  0.10  per  cent  for  each  foot, 
or  about  12,000  pounds  of  humus-nitrogen  per  acre  in  the  three 
feet.  The  Santa  Rosa,  Yountville,  and  Vacaville  soils  are  nearly 
equal  in  their  amounts  of  0.08  per  cent.  In  the  entire  column 
of  twelve  feet,  the  percentage  of  humus-nitrogen  is  greatest  in 
the  Santa  Rosa  alluvial  (0.05  per  cent),  while  in  the  Russian 
River  alluvial  and  the  Vaca  Valley  soils  the  percentage  is  0.04 
per  cent.  This  high  amount  of  humus-nitrogen  in  these  soils 
becomes  gradually  available  to  plants  only  through  the  action  of 
bacteria. 

The  soils  of  the  valleys  north  of  the  bay  region  may  then  be 
considered  as  being  well  supplied  in  humus  and  humus-nitrogen, 
which  is  well  distributed  throughout  a  depth  of  ten  or  twelve 
feet,  thus  affording  special  inducements  for  deep  rooting  and 
deep  feeding  of  plants. 

The  Bay  Region 

Alameda  Plains. — The  bay  shore  rises  gently  eastward  to  the 
foot  of  the  Contra  Costa  Hills,  a  distance  of  about  two  miles. 
On  this  slope  the  soil  is  largely  of  an  adobe  clay  nature.  The 
city  of  Berkeley  is  situated  on  this  slope,  the  University  of 
California  being  at  the  foot  of  the  hills.  A  column  of  the  clay 
adobe  was  taken  from  the  economic  garden  on  the  University 
grounds.  Southward  from  Berkeley  and  Oakland  the  slope 
widens  into  a  plain  traversed  by  streams  from  the  Coast  Range 
bordered  by  wide  bands  of  a  more  loamy  soil,  and  upon  it  are 
found  extensive  farms.  A  column  of  the  loam  was  taken  from 
the  land  of  Mrs.  Sanborn,  south  of  Niles,  and  another  from  the 
Meek  place  near  Hay  ward. 

These  are  excellent  soils,  with  fair  humus  and  humus-nitrogen. 
The  Berkeley  adobe  is  rich  in  nitrogen  throughout. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         215 


Table   20. — Humus   in   Soil  Columns  of   Alameda  Plai 

Berkeley  Hayward 

Humus-  Humus- 
Soil  Nitrogen  in             Soil  Nitrogen  in 

Clav  31.93  , A ,  Clay  9.21                          , * > 

Ft.                           Humus  Humus  Soil                                Humus  Humus  Soil 

1  Black  clay  ....    2.13  6.67      .14  Loam 1.81  4.65      .08 

2  Black  clay  ....    2.07  5.97      .12  Loam 1.04  5.67      .06 

3  Black  clay  ....    1.84  7.33      .14  Loam 74  6.26      .05 

4  Black  clay  ....    1.90  4.68      .09  Loam 80  4.73      .04 

5  Yellow  clay..       .95  7.05      .07  Loam 92  4.58      .04 

6  Yellow  clay..     1.06  5.37      .06  Loam 78  6.48      .05 

7  Yellow  clay..       .48  16.45      .08  Loam 68  6.18      .04 

8  Yellow  clay..       .37  24.10      .09  Loam 57  5.26      .03 

9  Yellow  clay..       .36  12.50      .05  Loam 38  7.90      .03 

10  Yellow  clay..       .36  14.70      .05  Sandy 32  6.58      .02 

11  Yellow  clay..       .45  9.35      .04  Dark  loam 41  6.85      .03 

12  Yellow  clay..       .49  8.16      .04  Dark  clay 80  1.28      .01 

Sum  of  per  cents  12.46  9.25 

Average  per  foot     1.04  10.20      .08                                      .77  5.53      .04 

Upper  3  feet :  * 
Sum  of  per  cents     6.04  3.59 

Average  per  foot     2.01  6.70      .13                                    1.19  5.60      .06 

*  Range  of  most  annual  plant  roots. 


ns,   Alameda   County 

NlLES 

Soil 
Clav  10.76 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

Dark  loam  . 

...    1.10 

5.36 

.06 

Dark  loam  . 

...   1.00 

4.20 

.06 

Dark  loam  . 

...      .78 

5.04 

.04 

Dark  loam  . 

...      .56 

5.01 

.03 

Dark  loam  . 

...      .44 

5.74 

.03 

Dark  loam  . 

...      .38 

5.17 

.02 

Dark  loam  . 

...      .40 

5.27 

.02 

Dark  loam  . 

...      .62 

8.15 

.05 

Dark  loam  . 

...      .70 

4.01 

.03 

Dark  loam  . 

...      .68 

4.54 

.03 

Dark  loam  . 

...      .56 

4.51 

.03 

Dark  loam  . 

...      .46 
7.68 

6.10 

.0? 

.64 

5.25 

.03 

2.88 

.96 

4.90 

.05 

East  of  Contra  Costa  Hills. — Eastward  across  the  Contra 
Costa  hills  several  narrow  valleys  connect  the  large  and  fertile 
Livermore  Valley  with  the  bay  shore  on  the  north,  and  repre- 
sentative columns  of  soils  were  taken  from  three  of  these. 

Ignacio  Valley. — Along  Walnut  Creek  there  is  a  narrow  belt 
of  black  clay-loam  soil  bordered  by  land  more  adobe-like  in 
nature  which  extends  to  the  low  mesa  and  hills.  The  higher  land 
on  the  mesa  and  bordering  it  in  the  valley  has  a  stiff  and  black 
adobe  clay  soil  about  three  feet  in  depth  and  underlaid  by  a 
whitish  material.  The  column  of  the  former  was  obtained  from 
the  place  of  Professor  F.  T.  Bioletti,  one  mile  north  of  Walnut 
Creek,  Contra  Costa  County. 

San  Ramon  Valley. — This  valley  is  a  continuation  southward 
of  Walnut  Creek  Valley,  but  wider  and  with  more  extensive 
black  adobe  soils,  a  column  of  which  was  obtained  in  the  vicinity 
of  San  Ramon  post  office.  Contra  Costa  County. 


216  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Livermore  Valley. — The  soil  of  the  valley  is  a  loam  while  that 
of  the  low  hills  of  the  west  and  south  is  reddish  and  gravelly. 
A  column  was  taken  to  a  depth  of  ten  feet  from  the  plain  in  the 
Santa  Rita  region,  Alameda  County. 


Table  21. 

— Humus  ix 

Soil 

COLUMXS 

of  Valleys  East 

of  Coxtra  Costa 

Hills 

Igxacio  Valley 

Sax  R. 

vmox  Valley 

Livermore  Valley 

CONTRA    COSTA 

COUNTY 

CONTRA 

COSTA    COUNTY 

ALAMEDA  COUNTY 

Walnut  Creek 

San  Ramon 

Santa  RiTi> 

L 

Soil 
Clay  35.02 
Ft.                           Humus 

Humus- 
Nitrogen  in 

Humus  Soil 

Soil 
Clay  41.00 

Humus 

Humus- 
Nitrogen  in 

Humus  Soil 

Soil 
Clay  10.60 

Humus 

Humus- 
Nitrogen  in 

Humus  Soil 

1  Black  clay  .... 

1.42 

5.73 

.08 

Black  clay 

...    1.23 

5.45 

.07 

Sandy  loam  .. 

.64 

8.78 

.06 

2   Black  clay  .... 

1.44 

4.96 

.07 

Black  clay 

...    1.28 

4.38 

.06 

Sandy  loam  .. 

.83 

6.03 

.05 

3    Black  clay  .... 

1.16 

5.81 

.06 

Black  clay 

...    1.08 

4.17 

.05 

Sandy  loam  .. 

.55 

5.62 

.03 

4   Black  clay  .... 

1.12 

5.01 

.06 

Black  clay  . 

...      .84 

4.29 

.04 

Sandy  loam  .. 

.45 

3.10 

.02 

5   Black  clay  .... 

1.08 

5.20 

.05 

Gray  clay... 

...       .81 

Reddish  loam 

.34 

3.23 

.01 

6   Black  clay  .... 

.70 

7.22 

.04 

Gray  clay... 

...      .75 

Reddish  loam 

.37 

3.78 

.01 

7   Black  clay  .... 

.60 

6.08 

.04 

Gray  clay- 

...      .29 

Reddish  loam 

.43 

2.57 

.01 

8   Black  clay  .... 

.60 

6.32 

.03 

Gray  clay... 

...       .20 

Sand 

.24 

3.33 

.01 

9  Black  clay  .... 

.42 

7.35 

.03 

Gray  clay... 

...       .14 

Sand 

.28 

2.14 

.01 

10   Black  clay  .... 

.52 

6.75 

.04 

Gray  clay... 

...      .12 

Sand 

.33 

4.25 

.01 

11   Black  clay  .... 

.36 

6.63 

.02 

Gray  clay... 

...       .09 

12   Black  clay  .... 

.26 

5.40 

.01 

Gray  clay... 

...      .07 

Sum  of  per  cents 

9.68 

6.90 

4.46 

Average  per  foot 

.80 

6.04 

.04 

.57 

4.57 

.05 

.45 

4.28 

.02 

Upper  3  feet :  * 

Sum  of  per  cents 

4.02 

3.59 

2.02 

Average  per  foot 

1.34 

5.50 

.07 

1.19 

4.70 

.05 

.67 

6.81 

.04 

Range  of  most  annual  plant  roots. 


In  these  two  groups  of  six  soils,  the  adobe  clay  from  Berkeley 
is  the  richest  in  every  respect,  while  that  from  Walnut  Creek 
is  next.  High  percentages  of  humus  are  found  to  a  greater  depth 
in  them  than  in  any  other  of  the  columns.  The  Berkeley  clay 
changes  color  below  the  fourth  foot  from  black  to  yellow,  while 
that  from  Walnut  Creek  remains  dark  throughout  its  twelve 
feet.  The  same  change  from  black  to  gray  occurs  in  the  San 
Ramon  adobe  below  the  fourth  foot,  and  each  of  its  upper  three 
feet  contains  more  than  1  per  cent  of  humus.  A  change  from 
dark  to  red  occurs  in  the  loam  soil  of  Santa  Rita  in  Livermore 
Valley. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         217 

The  humus  in  the  Berkeley  clay  is  surprisingly  rich  in 
nitrogen — that  of  the  eighth  foot  reaching  24  per  cent — but 
otherwise  the  general  average  of  the  entire  column  is  10.20  per 
cent,  which  is  higher  than  has  been  thus  far  observed  in  any  of 
the  columns  except  the  tule  marsh  of  Stockton.  The  percentage 
of  nitrogen  in  the  humus  of  the  other  five  columns  is  not  especi- 
ally high.  For  the  upper  three  feet  of  the  Berkeley  column  the 
average  of  humus-nitrogen  in  the  soil  is  0.13  per  cent,  or  approxi- 
mately 5200  pounds  for  each  foot.  This  is  a  high  amount  and 
is  probably  largely  due  to  the  excellent  cultivation  the  soil  has 
had  for  years  past. 

The  percentage  of  humus  in  the  sandy  loam  soil  taken  near 
Santa  Rita  in  the  central  part  of  Livermore  Valley  is  surprisingly 
low  in  the  upper  part  of  the  column,  and,  as  a  result,  the  sur- 
face was  found  dry  and  crusted  over  to  such  an  extent  that 
it  had  to  be  broken  up  before  the  auger  could  be  used.  Green- 
manure  crops  should  be  grown  and  turned  under  for  several 
successive  years  in  this  soil,  for  by  this  the  texture  of  the  soil 
would  be  improved,  more  nitrogen  introduced,  and  better  crops 
obtained.  A  comparison  of  the  soils  of  the  two  sections  shows 
that  those  of  the  bay  shore  are  richer  in  humus  and  in  nitrogen, 
both  in  the  surface  foot,  in  the  surface  three  feet,  and  in  the 
entire  column,  than  those  east  of  the  Contra  Costa  hills. 


South  of  the  Bay  Region 

Santa  Clara  Valley. — This  valley,  reaching  from  the  Bay  of 
San  Francisco  southward  for  seventy  miles  into  San  Benito 
County  has  a  variety  of  soils.  Around  the  bay,  back  from  the 
salt  marshes,  there  is  a  black  clay  adobe.  A  column  of  this  was 
taken  from  the  Morse  Seed  Farm  near  Santa  Clara. 

South  of  San  Jose  the  lands  are  more  loamy  in  character  and 
are  represented  by  a  column  taken  from  near  Gilroy,  by  Mr.  F. 
E.  Johnson. 

The  valley  west  of  San  Jose  has  a  soil  more  sandy  in  nature 
and  more  or  less  gravelly,  on  which  is  located  extensive  orchards. 
A  column  of  this  soil,  seemingly  representative  of  this  land,  was 
taken  from  the  El  Quito  ranch  south  of  Saratoga. 


218  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


Table  22- 

-Humus  in  Soil  Columns  of 

Santa  Clara 

Valley,  Santa  Clara  County 

Morse  Seed-Farm,  Santa  Clara 

Ei 

Quito 

GlLROY 

Soil 
Clay  58.85 
Ft. 

Humus 

Humus- 
Nitrogen  in 

Soil 
C1       10.74 

Humus 

Humus- 
Nitrogen  in 

Soil 
Clay  23.05 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

Humus  Soil 

Humus  Soil 

1   Black  clay  .... 

4.43 

2.78 

.12 

Dark  loam  .. 

..     .75 

4.80 

.04 

Black  clay  . 

...    2.76 

5.60 

.15 

2   Black  clay  .... 

3.66 

1.15 

.04 

Dark  loam  .. 

.      .66 

3.78 

.03 

Black  clay . 

...    2.12 

5.17 

.11 

3   Black  clay  .... 

2.80 

1.30 

.03 

Dark  loam  .. 

..      .96 

2.08 

.02 

Black  clay  . 

...    1.80 

4.68 

.08 

4   Gray  clay 

.61 

Dark  loam  .. 

..     .80 

2.25 

.02 

Black  clay  . 

...    1.40 

4.81 

.07 

5   Gray  clay 

.27 

Dark  loam  .. 

..      .63 

1.74 

.01 

Black  clay  . 

...      .96 

5.27 

.05 

6   Gray  clay 

.20 

Dark  loam  .. 

..      .61 

2.13 

.01 

Black  clay  . 

...      .70 

7.62 

.05 

7   Gray  clay 

.62 

Dark  loam  .. 

..      .73 

1.92 

.01 

Dark  clay... 

...      .68 

5.78 

.04 

8   Gray  clay 

.23 

Dark  loam  .. 

..      .62 

2.26 

.01 

Dark  clay.. 

...      .76 

6.28 

.05 

9   Gray  clay 

.30 

Dark  loam  .. 

..      .25 

Dark  clay.. 

...      .60 

4.68 

.05 

10   Gray  clay 

.13 

Dark  loam  .. 

.      .22 

Dark  clay- 

...      .62 

4.53 

.03 

11 

Gravel 

Dark  clay- 

...     .58 

4.36 

.03 

12 

Dark  clay.. 

...      .68 

3.72 

.03 

Sum  of  per  cents  13.25 

6.23 

13.66 

Average  per  foot 

1.33 

.62 

2.62 

.02 

1.14 

5.21 

.06 

Upper  3  feet :  * 

Sum  of  per  cents  10.89 

2.37 

6.68 

Average  per  foot 

3.63 

1.74 

, 

06 

.79 

3.55 

.03 

2.23 

5.15 

.11 

Range  of  most  annual  plant  roots. 


The  two  clay  soils  from  Santa  Clara  and  Gilroy  are  rich  in 
humus  to  depths  of  three  and  four  feet  respectively,  and  in  the 
latter  the  percentage  is  quite  large  through  the  entire  column. 

In  the  Santa  Clara  column  there  is  a  sudden  and  great  fall 
in  percentage  below  the  third  foot,  where  the  color  also  sharply 
changes  from  very  black  to  gray.  In  this  soil  the  clay  percentage 
is  very  high,  producing  such  a  compact  and  severe  texture  as 
to  prevent  the  downward  distribution  of  any  mass  of  plant  roots. 

The  El  Quito  soil,  if  a  true  representative  of  the  orchard 
lands  of  the  west  side  of  the  valley,  clearly  lacks  a  sufficient 
supply  of  humus  in  the  upper  surface  foot,  though  lower  down 
in  the  column  the  percentage  is  very  fair.  A  soil  from  Cupertino 
also  had  a  low  percentage  in  its  surface  foot;  the  humus,  how- 
ever, in  both  the  El  Quito  and  Santa  Clara  soil  is  surprisingly 
poor  in  nitrogen.  A  green-manure  crop,  rich  in  nitrogen,  is 
clearly  needed  to  produce  conditions  for  high  fertility.  The 
Gilroy  column  has  a  fair  amount  of  nitrogen. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         219 

Pajaro  Valley. — The  soil  of  the  valley  proper  is  a  dark  loam, 
while  along  the  river  are  adobe  clays  and  clay  loams,  the  latter 
being  largely  devoted  to  sugar-beet  culture.  The  valley  loam  is 
alone  represented  in  the  soil  column  series.  It  was  taken  from 
the  apple-growing  section  on  the  Watsonville  side  of  the  valley. 
Another  column  of  soil  was  taken  from  Watsonville  Heights, 
one  mile  northwest  of  the  town.  At  a  depth  of  eight  feet  a  mass 
of  decomposed  granite  was  reached.  Both  columns  were  taken 
by  Mr.  F.  E.  Johnson. 


Table  23. — Humus  in  Soil  Columns  from  near  Watsonville, 
Santa  Cruz  County 


Pajaro  Valley 

Heights 

Watsonville 

Watsonville 

Soil 
Clay  9.63 
Ft.                           Humus 

Humus- 
Nitrogen  in 

Soil 
Clay  16.50 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

Humus 

Soil 

1   Brown  loam.. 

1.38 

6.29 

.09 

Dark  loam  .. 

1.92 

4.80 

.09 

2   Loam 

.92 

4.87 

.05 

Dark  loam  .. 

1.46 

4.60 

.07 

3   Loam 

.94 

4.77 

.05 

Light  clay.... 

.       .50 

9.00 

.05 

4  Loam 

.74 

4.54 

.03 

Yellow  clay- 

.21 

6.70 

.01 

5   Loam 

.60 

4.67 

.03 

Yellow  clay- 

.       .11 

6.40 

.01 

6  Loam 

.60 

4.67 

.03 

Yellow  clay- 

.       .08 

7.50 

.01 

7   Loam 

.92 

4.57 

.04 

Gravelly  

.       .09 

8.90 

.01 

8   Loam 

.86 

3.26 

.03 

Gravelly  

.       .09 

4.80 

.01 

9   Loam 

.54 

5.19 

.03 

Hardpan 

10   Loam 

.62 

3.61 

.02 

11  Loam 

.24 

4.67 

.01 

12   Loam 

.46 

4.26 

.02 

Sum  of  per  cents 

8.82 

4.46 

Average  per  foot 

.74 

4.61 

.04 

.56 

6.60 

.03 

Upper  3  feet :  * 

Sum  of  per  cents 

3.24 

3.88 

Average  per  foot 

1.08 

5.31 

.06 

1.29 

6.13 

.07 

:  Range  of  most  annual  plant  roots. 

The  soil  of  the  valley  is  deeper  than  that  of  the  Heights,  but 
the  percentages  of  humus  in  the  first  foot  and  in  the  upper  three 
feet  are  not  as  great;  neither  is  its  humus  so  rich  in  nitrogen. 
The  total  amount  of  humus  in  the  Pajaro  Valley  column  is  very 
good  in  its  distribution  downward  and  this,  with  the  sandy  loam 
nature  of  the  soil,  gives  encouragement  to  the  deep  rooting  of 


220  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

plants  in  their  search  for  food  and  moisture.  The  general 
average  of  nitrogen  in  the  soil  is  good  in  the  upper  three  feet 
where  it  is  most  needed. 

Salinas  Valley. — The  lower  or  northern  part  of  the  valley  for 
about  fifty  miles  is  from  eight  to  twelve  miles  wide,  but  to  the 
southward  the  valley  is  very  narrow.  Two  classes  of  soil  are 
represented  in  this  series:  a  column  of  fifteen  feet  from  the 
sandy  loam  lands  of  the  west  side  of  the  Salinas  River  at  Fort 
Romie  near  Soledad;  a  column  of  the  black  adobe  lands  around 
King  City,  Monterey  County,  was  kindly  sent  by  Mr.  R.  L. 
Adams,  formerly  of  the  Spreckels  Beet  Sugar  Company. 


Table  24. — Humus  in  Soil  Columns  of  Salinas  Valley, 
Monterey  County 


Ft. 

ROMIE 

King  City 

Soil 
Clay  6.83 
Ft. 

Humus 

Humus- 
Nitrogen  in 

Humus  Soil 

Soil 
Clay  32.90 

Humus 

Humus- 
Nitrogen  in 

Humus  Soil 

1   Sandy 

1.08 

6.76 

.07 

Adobe  clay  .. 

1.15 

2.69 

.03 

2   Sandy 

.73 

8.46 

.06 

Adobe  clay  .. 

.94 

3.43 

.03 

3    Sandy 

.50 

7.30 

.04 

Adobe  clay  .. 

.61 

3.90 

.02 

4   Sand 

.33 

12.77 

.04 

Sandy 

.       .25 

5.04 

.01 

5   Loam 

.     .78 

5.76 

.05 

Clay  loam 

.      .52 

5.39 

.03 

6   Loam 

1.02 

4.96 

.05 

Clay  loam 

.      .41 

2.73 

.01 

7   Loam 

.62 

4.53 

.03 

Clay  loam 

.      .43 

3.91 

.02 

8   Loam 

.70 

5.43 

.04 

Clay  loam 

.      .37 

3.41 

.01 

9   Loam 

.77 

5.32 

.04 

Clay  loam 

.      .33 

2.97 

.01 

10  Loam 

.77 

5.45 

.04 

Coarse  sand 

.11 

6.36 

.01 

11   Loam 

.44 

5.00 

.02 

Coarse  sand 

.00 

12   Loam 

.46 

4.79 

.02 

Coarse  sand 

.00 

13   Loam 

.36 

6.94 

.03 

14  Loam 

.34 

7.35 

.03 

15   Loam 

.41 

6.83 

.03 

Sum  of  per  cents 

in    15  feet 

9.31 

in   10  feet 

5.12 

Average  per  foot 

.62 

6.51 

.04 

.51 

3.98 

.02 

Upper  3  feet :  * 

Sum  of  per  cents 

2.31 

2.70 

Average  per  foot 

.77 

7.50 

.06 

.90 

3.34 

.03 

k  Range  of  most  annual  plant  roots. 

1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         221 

These  soils  are  very  different  in  texture,  that  of  Fort  Romie 
being  of  a  sandy  nature  throughout  eighteen  feet  or  more,  while 
that  from  King  City  is  a  stiff  clay  for  a  depth  of  three  feet, 
changing  to  sand  and  then  a  clay  loam.  The  effect  of  the 
presence  of  the  sand  is  shown  in  the  sudden  diminution  of 
humus  in  the  fourth  foot,  and  the  same  change  is  noted  in  the 
tenth  foot. 

The  deep  rooting  of  plants  is  more  marked  in  the  Fort  Romie 
soil  by  the  higher  percentages  of  humus  in  the  lower  half  of 
the  column.  The  humus  and  the  soil  are  each  also  richer  in 
nitrogen  than  that  of  the  King  City  clay,  which  clearly  would 
be  greatly  benefited  in  texture  and  richness  by  systematic  green- 
manuring  with  legumes. 

The  column  of  soil  from  Fort  Romie  was  continued  to  water 
at  fifteen  feet  and  humus  found  in  fair  amount  in  the  last  foot. 

Arroyo  Grande  Valley. — The  soil  of  this  narrow  but  important 
valley  is  of  a  dark  and  heavy  clay  loam  nature  to  the  depth  of 


Table  25. — Humus  in  Soil  Columns  of  Arroyo  Grande  Valley, 
San  Luis  Obispo  County 


Arroy< 

3  Grande 

Routzahx  Seed 

Farm 

Soil 
Clay  17.99 
Ft.                           Humus 

Humus- 
Nitrogen  in 

Humus  Soil 

Soil 
Clay  28.80 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

1   Black  loam.... 

2.50 

6.46 

.16 

Black  clay  .. 

...    3.78 

4.31 

.16 

2   Black  loam.... 

2.15 

4.67 

.10 

Dark  loam  . 

...    1.50 

4.96 

.07 

3   Black  loam.... 

1.83 

5.37 

.10 

Dark  loam  . 

...    1.18 

5.95 

.07 

4  Black  loam.... 

1.54 

5.65 

.09 

Dark  loam  . 

...    1.52 

3.88 

.06 

5   Dark  loam  .... 

1.64 

5.31 

.09 

Dark  loam  . 

...   1.34 

4.82 

.07 

6  Dark  loam  .... 

1.56 

4.68 

.07 

Light  clay... 

...      .64 

5.27 

.03 

7  Dark  loam  .... 

1.36 

6.30 

.09 

Light  clay... 

...    1.04 

5.67 

.06 

8  Dark  loam  .... 

.88 

8.30 

.07 

Light  clay... 

...      .70 

7.22 

.05 

9  Light  loam  .... 

.62 

6.36 

.04 

Light  clay... 

...      .84 

6.02 

.05 

10   Dark  clay 

.82 

5.48 

.05 

Light  clay... 

...      .96 

5.56 

.05 

11   Dark  clay 

.88 

5.11 

.05 

Light  clay... 

...      .76 

5.91 

.05 

12   Dark  clay 

.86 

5.22 

.05 

Dark  clay... 

...    1.20 

5.75 

.07 

Sum  of  per  cents  16.64 

15.46 

Average  per  foot 

1.39 

5.74 

.08 

1.29 

5.44 

.07 

Upper  3  feet:* 

Sum  of  per  cents 

6.48 

6.46 

Average  per  foot 

2.16 

5.50 

.12 

2.15 

5.07 

.10 

Range  of  most  annual  plant  roots. 


222  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

twelve  feet  and  more.  Two  columns  were  obtained  by  Mr.  F. 
E.  Johnson,  one  near  the  town  of  Arroyo  Grande,  the  other  from 
the  farm  of  the  Routzahn  Seed  Company,  a  few  miles  to  the 
westward,  the  only  apparent  difference  being  a  darker  color  in 
the  surface  foot  of  the  seed-farm  soil. 

The  soil  from  the  Routzahn  seed-farm  in  the  Arroyo  Grande 
Valley  is  certainly  remarkably  rich  in  humus  for  an  arid  soil; 
for  not  only  does  each  foot  of  the  upper  five  feet  and  also  the 
seventh  contain  more  than  1  per  cent,  but  the  twelfth  foot  has 
1.20  per  cent  and  the  tenth  nearly  1  per  cent.  The  soil  from 
near  the  town  of  Arroyo  Grande  is  even  richer  than  that  of  the 
seed-farm,  for  it  contains  not  only  more  than  1.50  per  cent  of 
humus  in  each  of  the  upper  seven  feet,  but  each  of  the  lower 
five  feet  lacks  but  little  of  having  1  per  cent. 

The  percentages  of  humus-nitrogen  in  these  soils  are  also  very 
high,  especially  in  the  upper  few  feet  of  each  column,  that  of 


Table  26. — Humus  in  Soil  Columns  of  Santa  Maria  and  Lompoc  Valleys, 
Santa  Barbara  County 


Santa  Maria  Valley 

SANTA   BARBARA  COUNTY 
West  op  Santa  Maria 


Lompoc  Valley 

SANTA  BARBARA  COUNTY 
Burpee  Seed-Farm 


Soil 

Clay  10.25 

Ft,                           ] 

Humus 

Humus- 
Nitrogen  in 

Humus  Soil 

Soil 
Clay  33.40 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

1   Dark  loam  .... 

1.44 

9.57 

.11 

Dark  clay... 

...    2.50 

5.28 

.13 

2   Dark  loam  .... 

1.11 

4.81 

.05 

Dark  clay- 

...    1.56 

4.62 

.07 

3   Dark  loam  .... 

.84 

5.52 

.05 

Dark  clay... 

...    1.51 

4.90 

.07 

4   Light  loam  .... 

.26 

9.72 

.03 

Dark  clay... 

...    1.93 

6.12 

.12 

5   Light  loam  .... 

.46 

7.76 

.04 

Dark  clay... 

...    1.07 

5.32 

.06 

6   Light  loam  .... 

.32 

8.97 

.03 

Dark  clay... 

...    1.18 

7.28 

.09 

7   Light  loam  .... 

.24 

9.36 

.02 

Dark  clay... 

...    1.33 

5.94 

.08 

8   Gray  loam 

.21 

11.36 

.02 

Dark  clay... 

...      .80 

6.13 

.05 

9   Gray  loam 

.     .21 

12.03 

.03 

Dark  clay... 

...      .43 

6.27 

.03 

10   Gray  loam 

.23 

9.77 

.02 

Dark  clay... 

...      .21 

8.58 

.02 

11   Gray  loam 

.09 

18.72 

.02 

Dark  clay... 

...      .24 

8.75 

.02 

12   Gray  loam 

.     .16 

17.15 

.03 

Dark  clay... 

...      .27 

8.53 

.02 

Sum  of  per  cents 

5.57 

13.03 

Average  per  foot 

.46 

10.40 

.04 

1.09 

6.50 

.05 

Upper  3  feet :  * 

Sum  of  per  cents 

3.39 

5.57 

A  v.  rage  per  foot 

1.13 

6.67 

.07 

1.86 

4.93 

.09 

Range  of  most  a 

nnual  p 

lant    root 

s. 

1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         223 

the  surface  foot  being  0.16  per  cent,  or  approximately  6400 
pounds  per  acre.  This  extreme  richness  in  humus  and  nitrogen, 
as  well  as  in  potash  and  phosphoric  acid,  is  responsible  for  the 
high  productiveness  and  the  national  reputation  the  valley 
enjoys  as  a  vegetable-seed  producing  region. 

Santa  Maria  Valley. — The  soil  is  chiefly  a  sandy  loam  of  a 
brownish  color  and  very  deep.  A  column  was  taken  by  Mr.  F. 
E.  Johnson  near  the  sugar-beet  fields  five  miles  west  of  the  town 
of  Santa  Maria. 

Lompoc  Valley. — Three  chief  classes  of  soils  occupy  the 
valley — adobe  near  the  hills,  sandy  alluvium  near  Santa  Inez 
River,  and  an  intermediate  type  of  clay  loam  between  them. 
The  Burpee  seed-farm  is  situated  on  the  clay  loam  lands,  and  a 
column  of  soil  was  taken  there  to  a  depth  of  twelve  feet,  at 
which  point  water  was  reached. 

Santa  Maria  Valley  soil  has  a  fair  amount  of  humus  in  the 
upper  three  feet  and  low  percentages  through  the  rest  of  the 
column,  and  this  humus  has  high  percentages  of  nitrogen.  The 
smaller  amounts  in  the  second  and  third  foot  may  be  due  to 
withdrawal  by  plant  roots.  The  general  average  of  organic 
nitrogen  in  the  upper  three  feet  of  soil  is  good,  but  for  the  entire 
column  the  percentage  is  low,  because  of  the  low  amount  of 
humus. 

In  strong  contrast  to  the  sandy  loam  soil  of  Santa  Maria 
Valley  is  the  heavier  clay  of  the  Lompoc  Valley  through  which 
flows  Santa  Inez  River.  The  upper  seven  feet  of  the  Burpee 
soil  each  contains  more  than  1  per  cent  of  humus,  and  this, 
though  not  especially  rich  in  nitrogen,  gives  to  the  soil  itself 
fairly  high  percentages,  the  average  in  the  upper  three  feet 
being  0.09  per  cent,  or  about  10,000  pounds  per  acre. 

Summary  of  Results  in  Coast  Range  Region 
The  soils  of  the  valleys  of  the  Coast  Range  are  remarkably 
high  in  their  humus  content  when  compared  with  the  other  soils 
of  the  arid  region.  The  general  average  of  the  state  is  1.25  per 
cent  in  the  surface  soil,  while  that  for  these  coast  valleys  is  1.94 
per  cent.  But  especially  does  this  difference  appear  when  we  note 
the  many  soils  in  which  more  than  1  per  cent  of  humus  is  found 


224  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

columns  there  is  a  decrease  downward,  indicating  that  the 
humifieation  was  of  plant  roots  rather  than  of  vegetable  matter 
deposited  from  overflow  as  the  land  was  being  built  up. 

A  comparison  of  the  results  of  the  examination  of  the  first 
foot  gives  an  average  of  2.08  per  cent  of  humus  north  of  the 
bay,  1.82  per  cent  for  the  bay  region,  and  1.93  for  the  region 
south,  while  for  the  three  upper  feet  the  averages  are  1.55,  1.59, 
and  1.45  per  cent  respectively.  This  shows  quite  a  close  agree- 
ment in  the  soils  of  the  valleys  of  the  three  divisions. 

A  glance  over  the  tables  brings  out  the  fact  that  the  Santa 
Clara  soil  has  a  higher  amount  of  humus  (4.43  per  cent)  in  the 
first  foot  than  any  soil  of  the  state,  except  the  marsh  soils,  and 
that  nine  of  the  twenty-five  columns  of  the  Coast  Range  have 
more  than  2  per  cent  in  the  surface  foot,  while  in  all  others  but 
two  there  is  more  than  1  per  cent. 

The  portion  of  the  soil  column  lying  below  the  first  foot  is 
richer  in  humus  than  that  of  other  agricultural  regions.  There 
is  more  than  1  per  cent  in  each  of  the  four  upper  feet  of  ten 
of  the  twenty-four  columns  of  the  Coast  Range;  in  the  columns 
from  Santa  Rosa,  Russian  River,  Walnut  Creek,  and  Berkeley 
this  percentage  extends  through  five  feet,  while  in  the  soil  from 
Lompoc  and  Arroyo  Grande  it  reaches  through  seven  feet. 

The  humus  of  the  Santa  Maria  soil  is  richest  in  nitrogen,  9.57 
per  cent,  that  of  Livermore  Valley  being  next  with  8.78.  The 
surface  soils  whose  humus  is  poorest  in  nitrogen  according  to 
the  analyses  are  King  City  and  Santa  Clara  adobes.  The  general 
average  for  the  twenty-four  columns  is  5.36  per  cent. 

The  percentage  of  nitrogen  in  the  surface  soil  is  highest  in 
the  soils  from  Arroyo  Grande,  viz.,  0.16  per  cent,  or  approxi- 
mately 6400  pounds  per  acre.  Gilroy  has  0.15  per  cent,  Berkeley 
0.14  per  cent,  Lompoc,  Vacaville,  and  Kenwood  0.13  per  cent 
each,  and  Santa  Clara,  El  Verano,  Santa  Maria,  and  Yountville 
each  has  more  than  0.10  per  cent. 

If  a  m  us  iii  the  Upper  Three  Feet. — The  percentage  of  humus 
in  the  upper  three  feet  has  a  summation  of  10.89  for  the  Santa 
( llara,  a  little  more  than  6  per  cent  for  Gilroy,  Berkeley,  and  the 
two  Arroyo  Grande  columns,  and  5.57  per  cent  for  Lompoc,  but 
all  others  are  below  this. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         225 

The  humus  of  the  upper  three  feet  of  the  Fort  Romie  soil 
is  richest  in  nitrogen,  7.50  per  cent,  while  that  of  the  Santa  Clara 
adobe  has  only  an  average  of  1.74  per  cent.  The  general  average 
of  all  of  this  portion  of  the  columns  is  5.00  per  cent,  although 
fourteen  of  the  twenty-four  have  a  higher  percentage. 

The  humus-nitrogen  in  this  portion  of  the  column  varies  from 
0.13  per  cent  in  the  Berkeley  adobe,  0.11  per  cent  in  the  soils 
from  Gilroy  and  Arroyo  Grande,  to  more  than  0.05  per  cent  in 
all  others  except  four. 

Humus  in  the  Entire  Column. — Nine  of  the  twenty-four 
columns  have  greater  amounts  of  humus  in  their  depths  of  ten 
or  twelve  feet  than  has  been  found  in  any  of  the  columns 
representing  other  parts  of  the  state.  The  two  columns  from  the 
Arroyo  Grande,  with  sums  of  16.74  per  cent  and  15.56  per  cent, 
have  the  highest  amounts  and  are  followed  in  the  order  of  highest 
by  Gilroy,  Santa  Clara,  and  Lompoc,  each  with  more  than  13.00 
per  cent,  and  Berkeley,  Russian  River  Valley,  Yountville,  Santa 
Rosa,  and  El  Verano,  each  with  more  than  11.00  per  cent. 

The  humus  of  the  entire  soil  columns  of  the  Coast  Range 
valleys  is  about  as  rich  in  organic  nitrogen  as  that  of  other  soils 
of  the  state,  the  highest  average  percentage  being  in  the  Santa 
Maria  soil  and  the  Berkeley  adobe,  10.40  and  10.21  per  cent 
respectively;  the  Kenwood  and  Lompos  soils  are  the  next  in 
amount,  with  7.79  and  6.50  per  cent  respectively.  The  Walnut 
Creek  column  has  an  average  of  6.04  per  cent,  but  all  other 
averages  are  below  6  per  cent  for  the  entire  column.  The 
organic  nitrogen  of  the  soil  itself  varies  from  0.08  per  cent  in 
the  Arroyo  Grande,  Berkeley,  and  Kenwood  columns,  0.07  per 
cent  in  the  Arroyo  Grande  seed-farm  to  0.05  per  cent  in  Santa 
Rosa,  Walnut  Creek,  San  Ramon,  and  Lompoc ;  but  all  others 
have  less. 


SOIL  COLUMNS  OF  SOUTHERN  CALIFORNIA 

The  region  known  as  Southern  California  embraces  that  part 
of  the  state  lying  south  of  the  Sierra  Madre  and  Santa  Ynez 
mountains  and  includes  a  number  of  large  and  fertile  valleys 
and  plains. 


226  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Saticoy  Plain. — The  long  and  broad  slope  in  Ventura  County, 
reaching  from  the  mountains  southward  to  the  sea-shore  and 
noted  for  its  lima  bean  culture,  is  represented  by  two  soil 
columns,  one  taken  by  Mr.  J.  B.  Neff  from  near  Mound  School- 
house,  a  few  miles  east  of  Ventura,  and  the  other  from  the  orange 
grove  of  Mr.  N.  B.  Blanchard,  at  Santa  Paula. 


Table  27. — Humus  in  Soil  Columns  of  Saticoy  Plains,  Ventura  County 

Mound  Schoolhouse  Santa  Paula 

Humus-  Humus- 
Soil                                Nitrogen  in  Soil  Nitrogen  in 

Clay  14.18                        , -*- N  Clav  15.02                        , * , 

Ft.                           Humus    Humus  Soil  Humus  Humus  Soil 

1  Loam 1.23           5.14      .06  Dark  loam....     1.23  5.61      .07 

2  Loam 1.36          4.96      .07  Dark  loam 84  6.90      .06 

3  Loam 52          5.67      .03  Dark  loam 53  6.60      .04 

4  Loam 57          6.84      .04  Light  loam 45  6.00      .03 

5  Loam 54          5.46      .03  Light  loam 23  11.30      .03 

6  Loam 48          5.27      .03  Light  loam 21  20.47      .04 

7  Loam 54          4.68      .03  Dark  loam 56  9.81      .06 

8  Loam 45          4.99      .02  Dark  loam 59  1.69      .01 

9  Loam 36          4.68      .02  Dark  loam 52  10.00      .05 

10  Loam 51          4.13      .02  Dark  loam 38  9.74      .04 

11  Loam 60          3.98      .02  Dark  loam 33  7.27      .02 

12  Loam 52          4.32      .02  Fine  gravel  ..       .24           

Sum  of  per  cents     7.68  6.11 

Average  per  foot       .64          5.01      .03  .51  8.67      .04 

Upper  3  feet :  * 

Sum  of  per  cents     3.11  2.60 

Average  per  foot     1.04          5.26      .05  .87  6.37      .06 

*  Range  of  most  annual  plant  roots. 


The  soil  from  Mound  is  the  better  of  these  two  from  Saticoy 
Plain,  because  of  the  higher  percentage  of  humus  in  the  column 
below  the  first  foot;  its  second  foot  is  richer  than  the  first,  and 
the  entire  amount  is  greater  than  in  the  Santa  Paula.  But  its 
humus  is  poorer  in  nitrogen  (5.01  per  cent)  than  that  of  Santa 
Paula  (8.67  per  cent),  and  the  soil  itself  is  not  so  well  supplied. 
The  upper  three  feet  of  each  column  has  a  fair  amount  of  soil 
nitrogen. 

It  would  naturally  be  supposed  that  the  growing  of  beans  for 
SO  many  years  and  leaving  the  roots  and  stubble  in  the  ground 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         227 

would  have  greatly  enriched  the  Mound  soil  with  nitrogen  from 
the  leguminous  crop,  but  it  seems  to  have  produced  but  little  if 
any  advantage  over  the  orange  orchard  land ;  in  fact,  the  humus 
of  the  latter  is  far  richer  in  nitrogen,  perhaps  because  of  the  use 
of  fertilizers. 

Santa  Clara  River  Delta. — This  comprises  a  broad  region  of 
dark  alluvial  land  and  contains  more  or  less  alkali  salts  in  places. 
Water  is  usually  found  at  a  depth  of  eight  or  ten  feet  below  the 
surface.  The  delta  is  noted  for  its  sugar-beet  culture.  A  column 
was  taken  near  Springville  by  Mr.  J.  B.  Neff  to  a  depth  of  eight 
feet,  at  which  water  was  reached. 

Pleasant  Valley  Hill  Slope. — This  column  was  taken  from  the 
sandy  slope  of  the  hills  north  of  the  Southern  Pacific  Railroad 
station  of  Camarillo. 


Table  28. — Humus  in  Soil  Columns  of  Hillside  and  Delta  of  Santa 
Clara  River,  Ventura  County 


Pleasant  Valley 

River  Delta 

Hillside, 

Camarillo 

Springville 

Soil 
Clay  7.01 
Ft.                           Humus 

1   Sandy 84 

Humus- 
Nitrogen  in 

Humus  Soil 

6.19      .05 

Soil 
Clay  7.72 

Dark  loam.. 

Humus 
..       .96 

Humus- 
Nitrogen  in 

Humus  Soil 
7.31      .07 

2   Sandy 

.75 

4.93      .04 

Dark  loam.. 

..       .58 

6.29      .04 

3   Sandy 

.37 

Dark  loam.. 

..       .42 

4.68      .02 

4   Sandy  

.33 

Sandy  

..       .20 

8.44      .02 

5   Sandy  

.33 

Sandy 

..       .14 

5.14      .01 

6   Sandy  

.20 

Sandy 

..       .18 

4.69      .01 

7   Sandy  

.18 

Silty 

..      .22 

5.11      .01 

8    Sandy  

.12 

Sand 

..       .14 

5.14      .01 

9   Sandy  

.17 



10   Sandy  

.13 

11   Sandy 

.13 

12   Sandy 

.11 

Sum  of  per  cents 

3.66 

2.84 

Average  per  foot 

.30 

.   34 

5.70      .02 

Upper  3  feet :  * 

Sum  of  per  cents 

1.96 

1.96 

Average  per  foot 

.65 



.65 

6.20      .04 

Range  of  most  annual  plant  roots. 


228 


Un  iversity  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


The  soil  from  Springville  in  the  delta  of  Santa  Clara  River 
is  not  so  rich  in  humus  as  its  dark  color  would  lead  one  to 
suppose,  and  the  entire  column  of  eight  feet  is  quite  light  though 
the  land  is  highly  productive.  A  soil  from  near  Oxnard  pre- 
viously examined  was  found  to  contain  as  much  as  1.60  per  cent 
of  humus,  and  it  would  seem  that  the  great  body  of  land  farther 
out  in  the  valley  is  richer  than  that  near  the  hills.  An  inter- 
esting example  of  the  penetration  of  plant  roots  and  their 
humification  in  a  sandy  soil  is  seen  in  the  column  from  the  hill- 
side slope  north  of  Camarillo  station  in  Pleasant  Valley.  It  is 
interesting  to  note  that  this  soil  in  the  three  upper  feet  has  the 
same  percentage  as  that  of  the  Springville  column,  although  so 
different  in  color  and  texture. 

San  Fernando  Valley. — The  valley  of  San  Fernando  lies  north 
of  Los  Angeles  and  includes  about  two  hundred  square  miles. 
Much  of  the  valley  on  the  east  is  covered  by  debris  of  cobble- 
stones, gravel,  and  sand  washed  from  the  canons  on  the  northeast, 

Table  29. — Humus  in  Soil  Columns  of  San  Fernando  Valley, 
Los  Angeles  County 


San  Fernando 

Mission 

San  Fernando 

Soil 
Clay  11.15 
Ft.                           Humus 

Humus- 
Nitrogen  in 

Soil 
Clay  8.56 

Humus 

Hurm 

Nitroge 

Humus 

1S- 

n  in 

Humus 

Soil 

Soil 

1   Loam 

1.08 

4.68 

.05 

Loam 

...       .72 

5.46 

.04 

2   Loam 

.70 

4.81 

.03 

Loam 

...       .54 

6.24 

03 

.70 
.54 

4.61 
4.16 

.03 
.02 

Loam 

Loam 

...       .50 
...       .44 

5.05 
6.38 

03 

4   Loam 

.03 

5   Loam 

.52 

3.51 

.02 

Loam 

...       .36 

5.46 

.02 

6  Loam 

.46 

3.66 

.02 

Loam 

...       .34 

5.37 

.02 

7   Loam 

.40 

5.62 

.02 

Loam 

...       .34 

5.37 

.02 

8  Loam 

.20 

4.21 

.01 

Loam 

...       .36 

4.68 

.02 

9  Loam 

.24 

3.51 

.01 

Loam 

...       .42 

4.35 

.02 

10  Loam 

.28 

3.01 

.01 

Loam 

...       .34 

5.78 

.02 

11   Loam 

.20 

4.21 

.01 

Loam 

...       .30 

5.62 

.02 

12   Loam 

.22 

3.83 

.01 

Loam 

...       .26 

5.40 

01 

Sum  of  per  cents 

5.54 

4.92 

Average  per  foot 

.46 

4.23 

.02 

.41 

5.43 

.02 

Upper  3  feet :  * 

Sum  of  per  cents 

2.48 

1.76 

Average  per  foot 

.83 

4.70 

.04 

.59 

5.58 

.03 

Range  of  most  animal  plant  roots. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         229 

but  the  rest  of  the  valley  has  sandy  and  sandy  loam  soils,  with 
some  heavier  clays  on  the  south. 

Two  columns  were  obtained  by  Mr.  F.  E.  Johnson — one  from 
the  sandy  lands  about  one-half  mile  north  of  Fernando  and 
representing  the  ''granitic  wash  land"  at  the  foot  of  the  hills; 
the  other  from  lowland  near  the  old  Mission  two  miles  west  of 
Fernando. 

The  two  soils  from  the  San  Fernando  Valley  are  quite  differ- 
ent in  their  percentages  of  clay  as  well  as  in  amounts  of  humus 
in  the  first  foot,  in  the  upper  three  feet,  and  in  the  entire  column, 
the  advantage  being  with  the  soil  from  near  San  Fernando.  The 
Mission  soil  is  more  sandy  because  of  the  wash  from  the  hills. 
While  the  humus  of  the  Mission  column  is  the  richer  in  nitrogen, 
the  two  are  equal  so  far  as  the  soil  is  concerned  and  are  much 
below  the  requirements  for  fertility. 

The  soil  from  San  Fernando  probably  is  similar  in  character 
to  that  of  the  large  olive  orchard  at  Sylmar,  a  few  miles  north 
near  the  foot  of  the  hills. 


Table  30. — Humus 


Monrovia 

Soil 
Clay  7.61 
Ft.                           Humus 

1   Sandy  loam.. 

.94 

2   Sandy  loam.. 

.58 

3    Sandy  loam.. 

.56 

4   Sandy  loam.. 

.62 

5    Sandy  loam.. 

.64 

6   Sandy  loam.. 

.48 

7  Sandy  loam.. 

.34 

8    Sandy  loam.. 

.26 

9    Sandy  loam.. 

.28 

10   Sandy  loam.. 

.30 

11   Sandy  loam.. 

.28 

12   Sandy  loam.. 

.28 

Sum  of  per  cents 

5.56 

Average  per  foot 

.46 

Upper  3  feet :  * 

Sum  of  per  cents 

2.08 

Average  per  foot 

.69 

in  Soil  Columns  of  San  Gabriel  Valley, 

Los  Angeles  County 

Covina 

Humus-  Humus- 
Nitrogen  in  Soil  Nitrogen  in 

, -*- N  Clay  6.84                          , -*- , 

Humus  Soil  Humus  Humus  Soil 

3.82   .04  Sandy  loam..   .58  5.31   .03 

3.77   .02  Sandy  loam..   .48  4.08   .02 

3.75   .02  Sandy  loam..   .46  4.26   .02 

3.54   .02  Sandy  loam..   .32  5.25   .02 

3.59   .02  Sandy  loam..   .30  5.60   .02 

3.13   .02  Sandy  loam..   .26  5.38   .01 

3.24   .01  Sandy  loam..   .24  5.83   .01 

3.07      .01                 Sandy 18  4.51      .01 

2.86      .01                 Sandy 16  4.38      .01 

2.67      .01                 Sandy 18  3.89      .01 

2.50      .01                 Gravelly 18  3.89      .01 

2.86      .01  Coarse  gravel       ....            

3.34 

3.24      .02  .28  4.75      .02 


.78      .03 


1.51 
.50  4.55      .02 


Range  of  most  annual  plant  roots. 


230  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

San  Gabriel  Valley. — This  valley  lies  east  of  Los  Angeles  and 
reaches  from  the  mountains  southward  to  the  alluvial  plains.  It 
is  watered  by  the  San  Gabriel  River  and  bordered  on  the  east  by 
the  Puente  Hills,  and  the  San  Antonio  debris  cone.  Its  soil  is  a 
sandy  loam.  A  column  of  soil  was  taken  by  Mr.  F.  E.  Johnson 
from  the  neighborhood  of  Covina  and  "represents  an  average  of 
all  of  the  different  soil  types."  Another  column  was  taken  by 
Mr.  Johnson  from  near  Monrovia  and  represents  the  heavier  type 
of  soil,  the  greater  part  of  which  is  sandy  and  gravelly  wash 
from  the  hills. 

These  soils  are  quite  deficient  in  the  necessary  amount  of 
humus  to  keep  them  in  good  physical  condition  and  to  furnish 
adequate  nitrogen  for  the  plants. 

Attention  of  orchard  growers  should  especially  be  given  to 
the  yearly  growing  and  turning  under  of  the  best  leguminous 
crop  available — a  crop  giving  large  yields  of  succulent,  easily 
decomposed  stems  and  leaves  and  containing  high  percentages 
of  nitrogen.  Until  a  fair  supply  of  humus  in  the  three  upper 
feet  are  secured  by  this  method,  it  seems  necessary  to  apply 
nitrogen  fertilizers  to  the  trees  with  sufficient  irrigation  water 
to  carry  them  down  to  the  feeding  roots  at  a  depth  of  several 
feet  below  the  surface. 

San  Bernardino  Valley. — The  eastern  portion  of  the  valley  of 
Southern  California  known  as  the  San  Bernardino  Valley  is 
separated  from  the  western  by  a  range  of  low  hills  and  by  the 
debris  cone  of  the  San  Antonio  Creek,  which  issues  from  its 
valley  just  above  Pomona  and  supplies  most  of  the  water  to 
Chino  Creek  which  empties  into  the  Santa  Ana  River.  In  the 
past  from  time  to  time,  a  portion  of  the  San  Antonio  flow  has 
been  diverted  into  the  San  Gabriel. 

The  valley  covers  a  large  area  and  comprises  a  large  variety 
of  soil  types,  a  few  of  which  are  represented  by  soil  columns. 
The  valley  slopes  toward  the  south  to  the  Rincon  Basin  and 
Santa  Ana  River,  and  is  bordered  by  a  rim  of  mesa  land  on  the 
north,  east,  and  south. 

The  Valley  Plains. — The  soils  in  the  central  part  of  the  valley 
are  chiefly  of  a  sandy  nature,  of  excellent  depth  and  good  fer- 
tility.   The  lowlands  are  usually  highly  charged  with  alkali  that 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns 


231 


has  been  brought  in  by  drainage  from  the  higher  valley.  Several 
types  of  soil  from  the  plains  are  represented  in  the  columns. 

Sandy  loam  soils  of  the  central  part  of  the  valley  are  shown 
in  a  column  taken  by  Mr.  J.  W.  Mills  from  the  former  University 
of  California  Experiment  Station  tract  three  miles  southwest  of 
Ontario. 

Highly  sandy  soils,  apparently  accumulated  by  wind  storms 
blowing  in  from  the  mountain  passes  on  the  north,  lie  in  the 
central  part  of  the  valley  and  are  extensively  planted  in  grape 
vines,  the  roots  of  which  penetrate  downward  for  very  many 
feet.  A  column  of  this  type  of  soil  was  secured  at  Guasti  from 
the  land  of  the  Italian  Vineyard  Company. 

Alluvial  plains  of  the  Santa  Ana  Kiver,  known  as  the  Victoria 
Tract,  a  few  miles  east  of  San  Bernardino. 

The  soils  of  the  valley  plain  are  all  quite  sandy  and  contain 
but  small  amounts  of  humus  and  of  nitrogen.  The  tendency  to 
crust  over  and  to  form  a  sandy  hardpan  or  plowsole  near  the 
surface  is  quite  usual  with  these  soils.     A  succession  of  good 


Table  31.- 

-Humus  in 

Soil 

COLUM 

ns  of  Valley  Lands, 

San  Bernardino 

County 

SOUTHWEST 

of  Ontario 

Victoria  Tract 

Guasti 

Soil 
Clay  7.60 
Ft.                           Humus 

Humus- 
Nitrogen  in 

Soil 
Clav  8.38 

Humus 

Humus- 
Nitrogen  in 

Soil 
Clay  3.81 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

Humus 

Soil 

Humus  Soil 

1    Sandy 

.36 

4.68 

.02 

Loam.. 

.69 

4.92 

.03 

Sandy  — 

25 

3.36      .01 

2    Sandy 1. 

.22 

5.74 

.01 

Loam.. 

1.02 

4.62 

.05 

Sandy  .... 

18 

4.42      .01 

3    Sandy 

.19 

3.70 

.01 

Loam- 

.62 

2.26 

.01 

Sandy  .... 

14 

4.00      .01 

4   Sandy 

.13 

5.40 

.01 

Loam.. 

.37 

3.80 

.01 

Sandy  .... 

12 

5    Sand 

.10 

4.21 

.01 

Loam- 

.24 

2.92 

.01 

Sandy  .... 

09 

6   Sand 

.08 

3.51 

.01 

Loam. . 

.18 

2.22 

.01 

Sandy  .... 

08 

7    Sand 

.09 

3.12 

.01 

Sand  .. 

.16 

1.26 

Sandy  .... 

07 

8   Sand  

.06 

Sand  .. 

tr. 

Sandy  .... 

11 

9  Coarse  sand.. 

Coarse 

sand. 

Sandy  .... 

08 

10   Coarse  sand.. 

Coarse 

sand. 

Sandy  .... 

07 

11   Coarse  sand.. 

Coarse  sand. 

Sandy  .... 

07 

12   Coarse  sand- 

Coarse  sand. 

Sandy  .... 

07 

Sum  of  per  cents 

1.23 

3.28 

1.33 

Average  per  foot 

.10 

4.34 

.01 

.27 

3.00 

.01 

.11 



Upper  3  feet :  * 

Sum  of  per  cents 

.77 

2.33 

.57 

Average  per  foot 

.26 

4.70 

.01 

.78 

3.93 

.03 

.19 

3.92      .01 

Range  of  most  annual  plant  roots. 


232  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

green-manure  crops  grown,  turned  under  deeply,  and  allowed  to 
humify  properly  would  add  much  to  the  value  and  fertility  of 
these  lands. 

Low  Lands. — Near  the  border  of  Chino  Creek  there  are  low- 
lying  lands  forming  a  wide  border  of  "moist  lands"  which  do 
not  need  irrigation.  Ten  acres  of  this  near  Chino  formerly 
formed  a  part  of  the  Experiment  Station.  A  column  from  this 
was  taken  by  Mr.  F.  E.  Johnson.  Another  column  was  taken 
near  Pomona  from  a  marsh  spot  known  as  a  "cienega."  This 
is  a  "  limited  area  showing  growth  of  water-loving  plants,  appear- 
ing sporadically  in  otherwise  arid  surroundings — usually  hill- 
sides or  valley  margins — and  occasionally  giving  rise  to  flowing 
springs."—  (Kept.  Calif.  Expt.  Sta.,  1892-4,  p.  185.) 


Table  32. — Humus  in 


SAN  BERNARDINO 

Chino 

Soil 
Clay  13.44 
Ft.                           Humus 

1   Dark  silt 

2.31 

2   Dark  silt 

1.41 

3   Dark  silt 

.84 

4   Dark  silt 

1.05 

5   Blue  clay 

.72 

6   Blue  clay 

.82 

7   Blue  clay 

.78 

8 

9 

10 

11 

12 

Sum  of  per  cents 

7.93 

Average  per  foot 

1.13 

Upper  3  feet :  * 

Sum  of  per  cents 

4.56 

Average  per  foot 

1.52 

Soil  Columns  of  Lowlands,  San  Bernardino 
Valley 

COUNTY  LOS  ANGELES  COUNTY 

Pomona  Cienega 

Humus-  Humus- 
Nitrogen  in                      Soil  Nitrogen  in 

t *• «,  Marsh  , * ^ 

Humus  Soil                                          Humus  Humus  Soil 

4.86      .11                 Black  loam....    6.26  4.06      .25 

4.28      .06                 Black  loam....    3.12  3.50      .11 

5.52      .05                 Black  loam....    1.64  3.12      .05 

4.01      .04                 Sandy 72  18.30      .13 

6.14      .04                 Sand 12  2.33      .01 

5.65      .05                 Sand 66  2.12      .01 

5.38      .04                 Coarse  sand..       .15  2.00      .01 

Blue  sand 63  1.59      .01 

Blue  sand 61  1.31      .01 

Blue  sand 55  1.82      .01 

Blue  sand 30  2.32      .01 

Blue  sand 57  1.41      .01 

15.33 

5.12      .06                                             1.28  3.66      .05 


4.90      .07 
Range  of  most  annual  plant  roots. 


11.02 
3.67  3.56      .14 


In  each  of  these  lowland  soils  the  humus  content  is  excellent 
though  not  especially  rich  in  nitrogen.  The  large  amount  of  the 
former,  however,  makes  up  for  any  low  percentage  of  nitrogen 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns 


233 


and  gives  to  the  soil  an  adequate  amount,  especially  in  the  upper 
few  feet. 

The  Chino  soil  was  found  on  previous  examination  to  hold 
quite  high  amounts  of  alkali  salts,  among  which  was  nitrates  of 
soda  and  magnesia  (Rept.  Calif.  Expt.  Sta.,  1894-5,  p.  75). 

Mesa  Lands. — The  mesa  lands  that  border  the  valley  are 
largely  of  a  reddish  loam  type,  interspersed  on  the  north  side 
by  deposits  of  sand  and  gravel  from  the  hillsides. 

The  red  mesa  extends  eastward  up  the  San  Gorgonio  Pass  to 
its  summit  at  Banning,  where  it  forms  quite  a  high  plateau  above 
Timoteo  Canon. 

A  column  of  the  sandy  mesa  of  the  north  side  was  taken  in 
the  western  part  of  Highlands  to  a  depth  of  twelve  feet,  in  which 
the  sandy  soil  continued  to  the  bottom. 

A  column  representing  the  red  clay  mesa  was  taken  near 
Redlands  by  Mr.  F.  E.  Johnson.  The  upper  five  feet  was  of  a 
reddish  sandy  loam  nature,  below  which  it  changes  to  a  sandy 
clay  and  finally  to  a  gritty  material. 


Table  33  — 

Humus  in  Soil  Columns  of  North-side 

Mesa  of 

San  Bernardino  Valley 

Highlands 

Redlands 

Soil 
Clay  4.66 
Ft. 

Humus 

Humus- 
Nitrogen  in 

Soil 
Clay  10.33_ 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

Humus 

Soil 

1   Sandy  

.72 

6.25 

.05 

Red  loam 

..       .43 

5.88 

.03 

2    Sandy  

.46 

9.78 

.05 

Red  loam 

..       .33 

5.09 

.02 

3    Sandy  

.43 

7.90 

.03 

Red  loam 

..       .27 

5.20 

.01 

4   Sandy  

.37 

8.10 

.03 

Red  loam 

.22 

5.11 

.01 

5   Sandy  

.32 

7.18 

.02 

Red  loam 

.       .20 

5.75 

.01 

6   Sandy  

.28 

6.07 

.02 

Sandy  clay . 

.10 

8.42 

.01 

7    Sandy  

.27 

6.29 

.02 

Sandy  clay  . 

.10 

8.42 

.01 

8    Sandy 

.25 

6.80 

.02 

Sandy  clay  . 

.10 

8.42 

.01 

9   Sandy  

.25 

7.60 

.02 

Gritty 

..       .07 

7.00 

.01 

10    Sandy  

.22 

7.72 

.02 

Gritty 

.       .08 

7.00 

.01 

11    Sandy 

.14 

10.00 

.02 

Gritty 

.       .06 

12    Sandy 

.11 

17.27 

.02 

Gritty 

.       .07 

Sum  of  per  cents 

3.82 

2.03 

Average  per  foot 

.32 

8.41 

.03 

.17 

6.63 

.01 

Upper  3  feet:* 

Sum  of  per  cents 

1.61 

1.03 

Average  per  foot 

.54 

8.00 

.04 

.34 

5.39 

.02 

Range  of  most  annual  plant  roots. 


234  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

The  percentage  of  humus  in  each  of  the  above  soils  is  very 
low,  especially  in  that  of  the  red  loam  of  the  Redlands  mesa. 
The  percentages  decrease  steadily  into  the  lower  portions  of  each 
column. 

The  Highlands  sandy  soil  is  the  richer  of  the  two,  both  in 
humus  and  nitrogen,  and  in  the  entire  column  except  the  upper 
three  feet  is  fairly  supplied  with  each  of  these. 

The  Redlands  soil,  because  of  its  heavier  clay  nature,  would 
be  more  benefited  by  green-manuring  than  would  that  of  High- 
lands. 

South-side  Mesa. — On  the  south  side  of  the  valley  the  mesa 
rises  from  near  the  border  of  Santa  Ana  River  and  extends  to 
the  hills  at  elevations  much  above  the  plains.  The  soil  is  very 
generally  a  reddish  clay  loam,  more  or  less  gravelly,  and  overlies 
granitic  debris  at  depths  of  many  feet. 


Table  34. — Humus  in  Soil  Columns  of  South-side  Mesa  of 
San  Bernardino  Valley 


Corona 

Riverside 

Soil 
Clay  12.87 
Ft.                           Humus 

Humus- 
Nitrogen  in 

Soil 
Clay  11.78 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

Humus  Soil 

1  Red  loam 

.71 

7.91 

.06 

Red  loam.... 

..       .63 

4.00      .03 

2   Red  loam 

.41 

6.85 

.03 

Red  loam.... 

..       .30 

6.08      .02 

3   Red  loam 

.42 

4.68 

.02 

Red  loam.... 

..       .20 

6.32      .01 

4  Red  loam 

.25 

4.49 

.01 

Red  loam.... 

..       .11 

5.11      .01 

5   Gravelly 

.15 

5.62 

.01 

Red  loam.... 

..       .11 

5.11      .01 

6   Gravelly 

.14 

6.02 

.01 

Red  loam.... 

..       .12 

5.85      .01 

7  Gravelly 

.17 

3.30 

.01 

Red  loam.... 

..       .11 

5.11      .01 

8   Gravelly 

.26 

3.24 

.01 

Red  loam.... 

..       .10 

4.00      .01 

9   Gravelly 

.21 

4.01 

.01 

Red  loam.... 

tr. 

10   Gravelly 

.17 

3.30 

.01 

Red  loam.... 

11    Gravelly 

.18 

3.12 

.01 

Red  loam.... 



12   Gravelly 

.30 

3.74 

.01 

Red  loam.... 

Sum  of  per  cents 

3.37 

1.68 

Average  per  foot 

.28 

4.70 

.02 

.14 

5.19      .01 

Upper  3  feet :  * 

Sum  of  per  cents 

1.54 

1.13 

Average  per  foot 

.51 

6.48 

.04 

.09 

5.47      .02 

*  Range  of  most  annual  plant  roots. 


1914]       Loughridge :  Humus  and  Nitrogen  in  California  Soil  Columns         235 

A  column  from  Riverside  was  taken  from  Arlington  Heights 
orchard  lands  on  the  south,  with  the  assistance  of  Mr.  J.  H. 
Reed,  and  we  were  able  to  reach  a  depth  of  eighteen  feet  with 
comparative  ease. 

Another  mesa  soil  column  was  taken  by  Mr.  F.  E.  Johnson 
from  nearly  one  mile  south  of  the  town  of  Corona,  and  is  a  good 
representative  of  the  orchard  land  of  that  vicinity.  A  depth  of 
twelve  feet  was  reached  with  difficulty  because  of  the  presence 
of  much  gravel. 

The  red  mesa  land  on  the  south  side  of  the  valley  also  con- 
tains very  low  percentages  of  humus  and  of  nitrogen.  This  is 
especially  true  of  the  Riverside  soil,  more  than  one-half  of  whose 
supply  is  in  the  upper  two  feet.  Its  nitrogen  is  also  very  low. 
The  Corona  soil  is  somewhat  richer  in  nitrogen,  but  in  both  soils 
and  doubtless  on  the  rest  of  the  mesa,  the  need  of  good  green- 
manure  crops  for  the  production  of  humus  is  very  apparent. 

Los  Angeles  Alluvial  Plain, — The  three  rivers,  Los  Angeles, 
San  Gabriel,  and  Santa  Ana,  have  each  brought  down  from  the 
San  Bernardino  Mountains  large  quantities  of  silt,  sand  and 
clay  and  formed  a  large  body  or  region  of  alluvial  lands  known 
as  the  Los  Angeles  alluvial  plains.  Each  river  preserves  its 
own  course  through  these  plains  and  has  built  up  its  own  alluvial 
plain  with  its  own  material  independently  of  the  others.  We 
thus  find  that  the  soils  of  the  San  Gabriel  are  of  a  more  sandy 
nature  than  those  of  the  Santa  Ana,  probably  because  of  the 
more  rapid  velocity  of  the  river  current  over  a  shorter  distance ; 
the  Santa  Ana  leaves  the  mountains  east  of  San  Bernardino  and 
flows  by  a  circuitous  route  along  the  southern  side  of  the  valley 
and  thus  seems  to  have  left  much  of  its  coarse  material  behind 
and  deposited  chiefly  clays  and  silts  in  the  alluvial  plain. 

The  San  Gabriel  Plain  is  represented  by  three  columns.  One 
was  taken  from  the  place  of  Dr.  S.  S.  Twombly,  south  of  Fuller- 
ton,  to  a  depth  of  ten  feet;  another  from  the  place  of  Mr.  J.  B. 
Neff,  near  Anaheim;  while  the  third  column  was  taken  a  mile 
south  of  Compton. 

The  land  of  that  plain  belonging  to  the  San  Gabriel  and 
especially  between  this  and  the  Santa  Ana  River  is  greatly  varied 
in  character,  as  is  indicated  bv  these  three  columns.     In  some 


236  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


Table  35. — Humus   in   Soil  Columns   of   San  Gabriel  Kiver  Alluvial  Plain, 


Orange  County 


FULLERTON 

A.NAHEIM 

COMPTON 

Soil 
Clay  7.94 
Ft.                           Humus 

Humus- 
Nitrogen  in 

Humus  Soil 

Soil 
Clay  5.78 

Humus 

Humus- 
Nitrogen  in 

Humus  Soil 

Soil 
Clay  7.45 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

1    Loam... 

.51 

10.89 

.06 

Sandy 

88 

8.00 

.07 

Dark  loam... 

.     1.50 

6.77 

08 

2   Loam... 

.64 

7.82 

.05 

Sandy  

83 

6.46 

.05 

Dark  loam... 

.       .91 

9.16 

.05 

3    Loam... 

.25 

18.40 

.05 

Sandy 

68 

6.91 

.05 

Dark  loam... 

.       .51 

6.50 

.04 

4   Loam... 

.22 

15.45 

.03 

Sandy 

49 

8.00 

.04 

Light  loam.. 

..       .60 

7.47 

.03 

5   Loam... 

.22 

20.45 

.05 

Sandy 

41 

6.09 

.03 

Dark  loam... 

.       .49 

5.18 

.09 

6   Loam... 

.26 

10.77 

.03 

Sandy 

33 

6.06 

.02 

Light  loam.. 

..       .53 

7.25 

.04 

7   Loam... 

.33 

15.15 

.05 

Sandy 

33 

4.58 

.02 

Light  loam.. 

..       .64 

5.17 

.02 

8   Loam... 

.29 

19.31 

.06 

Sandy 

.25 

4.40 

.01 

Light  loam.. 

..       .52 

7.00 

.02 

9   Loam... 

.29 

12.41 

.04 

Sandy 

22 

.38 

.01 

Fine  sand  ... 

.       .38 

12.30 

.02 

10   Loam... 

.29 

19.31 

.06 

Sandy 

24 

.28 

.01 

Fine  sand  ... 

.       .42 

5.80 

.02 

11 

Dark  loam... 

.       .49 

4.15 

.03 

12 

Dark  loam... 

.       .32 

3.18 

.01 

Sum  of  per 

cents 

3.30 

4.66 

7.31 

Average  per  foot 

.33 

15.00 

.05 

.46 

5.12 

.03 

.61 

6.66 

.04 

Upper  3 

feet  : * 

Sum  of  per 

cents 

1.40 

2.39 

2.92 

Average  per  foot 

.47 

12.40 

.05 

.79 

7.12 

.06 

.97 

7.50 

.06 

Range  of  most  annual  plant  roots. 


localities,  as  around  Compton,  the  soil  is  of  a  dark  sandy  loam 
nature,  quite  micaceous  and  contains  more  humus  than  elsewhere. 
The  Compton  column  is  fairly  well  supplied  with  humus  and 
nitrogen  throughout  the  depth  of  twelve  feet,  and  conditions 
seem  to  be  especially  favorable  for  deep  rooting  of  plants.  In 
other  localities  there  are  heavy  sandy  deposits  from  old  river 
overflows,  the  soil  of  which  while  quite  fertile  needs  humus  to 
give  it  a  stronger  texture. 

The  Anaheim  column  was  taken  from  a  walnut  orchard  whose 
owner  had  practiced  a  system  of  green-manuring  for  a  number 
of  years  with  good  results.  While  the  percentage  of  humus  is 
still  rather  low,  yet  it  contains  much  nitrogen  in  the  upper  por- 
tion of  tin1  column.  The  sandy  loam  soils  along  the  border  of 
this  alluvial  plain  near  Fullerton,  represented  by  a  column  a 
short  distance  south  of  town,  are  surprisingly  low  in  their  humus 
content,   but  the  humus   is  remarkably   rich    in   nitrogen,   not    in 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         237 

isolated  levels  as  often  occurs  in  other  soils,  but  throughout  the 
entire  column,  the  general  average  being  0.15  per  cent,  or 
approximately  6000  pounds  of  nitrogen  per  acre-foot  through  the 
entire  depth.  No  other  column  from  the  entire  collection  has 
a  similar  record.  Bacterial  activity  to  render  this  humus-nitrogen 
available  to  plants  should  make  unnecessary  the  use  of  nitrogen 
fertilizers. 

The  Santa  Ana  Alluvial  Plain  is  represented  by  two  columns 
taken  by  Mr.  F.  E.  Johnson.  One  of  these  from  two  miles  south 
of  Santa  Ana,  represents  a  considerable  area  of  heavy  black 
adobe;  the  other,  from  Irvine  Station  six  miles  southeast  of 
Santa  Ana,  represents  a  lighter  clay  loam  soil.  Both  of  these 
columns  are  from  the  south  side  of  Santa  Ana  River. 


Table  36. — Humus  in  Soil  Columns 
Plain,  Orange 

Santa  Ana 

Humus- 
Soil  Nitrogen  in 

Clay  25.01  , -*- N 

Ft.  Humus    Humus  Soil 

1  Black  clay ....    2.42  3.71  .09 

2  Black  clay  ....    1.44  3.51  .05 

3  Black  clay  ....    1.02  4.80  .05 

4  Light  clay 83  5.90  .05 

5  Light  clay  ....       .76  2.22  .02 

6  Light  clay 46  2.75  .01 

7  Light  clay 31  2.72  .01 

8  Light  clay 22  2.55  .01 

9  Sandy 12  2.34  tr. 

10  Sandy 14  3.01 

11  Sandy 14  3.01       .... 

12  Sandy 20  4.18 

Sum  of  per  cents  8.06 

Average  per  foot  .67  3.40      .03 

Upper  3  feet :  * 

Sum  of  per  cents  4.88 

Average  per  foot  1.63  4.00      .06 

*  Range  of  most  annual  plant  roots. 


of  Santa  Ana  River  Alluvial 
County 

Irvine 

Humus- 
Soil  Nitrogen  in 

Clay  18.31  , -*- , 

Humus  Humus  Soil 

Clay  loam 70  5.86      .04 

Clay  loam 50  8.40      .04 

Clay  loam 44  4.09      .02 

Clay  loam 38  3.42      .01 

Clay  loam 34  1.76      .01 

Sand 22  1.82      .01 

Sand 19  .63      .01 

Sand 20  1.50      .01 


2.97 
.23  3.43      .02 


1.64 
.55  6.12      .03 


The  adobe  clay  of  Santa  Ana  contains  a  fair  amount  of 
humus,  but  the  humus  is  very  poor  in  nitrogen  throughout  the 
entire  column.     In  spite  of  the  latter  fact,  however,  the  per- 


238  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  ] 

centage  of  nitrogen  in  the  soil  is  fair,  especially  in  the  first  foot. 
The  loam  soil  from  Irvine  is  not  so  well  supplied  with  humus 
and  nitrogen  as  could  be  desired. 


Interior  Valleys 

The  immediate  coast  line  is  bordered  by  a  wide  mesa  which 
extends  south  to  the  state  line,  interrupted  by  the  characteristic 
deep  and  narrow  valleys  or  occasional  streams.  The  valley  of 
the  San  Diego  River  is  wide  and  affords  much  land  for  culture 
purposes.  The  mesa  reaches  eastward  in  width  to  the  foot  of  the 
higher  rolling  hills,  which  rise  still  higher  into  the  San  Jacinto 
Mountains.  Among  these  hills  lie  numerous  valleys,  small  and 
large,  whose  soils  are  rich  and  productive. 

Fallbrook  Mesa. — The  hills  are  for  the  most  part  somewhat 
rolling  and  capable  of  cultivation  whenever  the  soil  is  of  sufficient 
depth  and  extent.  Fallbrook  affords  an  example  of  these  cultiv- 
able hills  and  a  column  of  the  soil  was  taken  from  the  hillside 
vineyard  of  Loma  Ranch  south  of  the  town.  The  red  clay  loam 
soil  was  of  varying  thickness  and  underlaid  by  a  mass  of  dis- 
integrated granite. 

Perris  Valley  lies  southeast  of  Riverside  at  the  western  foot 
of  the  San  Jacinto  Mountains.  It  is  about  ten  miles  long  and 
six  wide,  and  has  a  variety  of  soils,  as  described  by  Professor 
Hilgard  in  the  Annual  Report  of  the  Agricultural  Experiment 
Station  for  1894-95.  The  heavier  soil  from  the  center  of  the 
valley,  about  a  mile  east  of  the  town  of  Perris,  was  selected  and 
a  column  taken  by  Mr.  F.  E.  Johnson. 

The  Valley  of  Escondido  is  a  large  and  productive  valley 
lying  near  the  mountains.  Its  soil  is  a  loam.  A  column  was 
taken  to  a  depth  of  twelve  feet  by  Mr.  F.  E.  Johnson  in  the 
vineyard  of  C.  C.  Katzenburger  on  the  north  side  of  the  valley. 

El  Cajon  Valley  lies  among  the  high  mountains  twenty-nine 
miles  east  of  San  Diego  and  has  an  area  of  six  by  four  miles. 
The  land  is  a  reddish  sandy  loam  and  is  very  productive.  A 
column  twelve  feet  in  depth  was  taken  from  near  the  cross- 
roads  by  Mr.  F.  E.  Johnson. 


1914]       Loughridge:  Humus  and  Nitrogen  in  Calif ornia  Soil  Columns         239 


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240  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

The  surface  soil  of  the  column  taken  near  Perris  is  badly 
deficient  in  humus,  but  in  each  of  the  three  feet  below  there  is 
a  fair  percentage.  Green-manuring  crops  are  called  for.  The 
hill  lands  of  Fallbrook  also  are  low  in  their  percentages  of 
humus  and  nitrogen  and  need  nitrogen  fertilizers  (either  through 
nitrates,  stable  manure,  tankage,  or  dried  blood)  as  well  as  good 
green-manure  crops. 

The  column  representing  the  Escondido  Valley  is  very  poor 
in  humus  and  nitrogen,  while  that  of  El  Cajon  is  better  supplied, 
though  still  much  below  what  is  needed  for  good  texture  and 
fertility.  Crops  should  respond  to  nitrate  fertilization  on  both 
of  these  soils. 

The  humus  in  all  of  these  soils  is  surprisingly  low  for  valley 
lands  that  are  as  productive  as  these. 

Summary  for  Southern  California  Soil  Columns 

The  following  are  the  averages  obtained  by  combinations  of 
the  twenty-six  columns,  omitting  the  marsh  of  the  Pomona 
cienega : 

Per  cent 

Average  humus  in  surface  foot  0.88 

Average  sum  of  per  cents  of  humus  in  upper  three  feet 1.98 

Average  humus  in  each  of  upper  three  feet  0.66 

Average  nitrogen  in  humus  of  surface  foot  5.53 

Average  nitrogen  in  humus  of  upper  three  feet  5.22 

Average  nitrogen  in  surface  foot  of  soil  0.05 

Average  nitrogen  in  upper  three  feet  of  soil  0.04 

Average  nitrogen  in  each  of  twelve  feet  of  soil  0.02 


These  percentages  are  all  too  low  and  indicate  the  great  need 
of  good  green-manuring  treatment  for  a  number  of  years  to 
build  up  the  upper  three  feet  of  soil  into  a  high  fertility.  This 
is  needed  more  than  phosphate  fertilization. 

There  are  but  six  of  the  twenty-five  soils  whose  surface  foot 
contains  more  than  1  per  cent  of  humus ;  there  are  but  five  others 
that  have  more  than  0.75  per  cent,  and  there  are  five  whose 
humus  falls  even  below  0.50  per  cent. 

The  lands  represented  by  these  columns  from  Southern 
California  are  under  such  continuous  cultivation  that  the  surface 
fool  is  hardly  a  proper  unit  of  comparison;  a  depth  of  three  feet 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         241 

would  be  more  nearly  correct,  for  in  that  is  usually  found  the 
mass  of  feeding  roots,  and  no  disturbing  irregular  conditions 
exist.  The  general  average  of  the  total  amount  in  the  three  upper 
feet  (sum  of  per  cents)  of  the  columns  (omitting  that  of  the 
Pomona  cienega)  is  1.98,  or  an  average  of  0.66  per  foot.  This 
is  too  small. 

The  Santa  Ana  adobe  and  Chino  moist  land  have  each  above 
4.50  and  Mound  Schoolhouse  has  3.11  per  cent,  but  all  others 
fall  below  the  latter.  Six  of  the  columns  have  more  than  2  per 
cent  each,  while  on  the  other  hand  three  have  each  a  sum  of 
less  than  1  per  cent  in  the  three  feet,  or  an  average  of  but 
0.25  per  cent  per  foot. 

The  humus  in  these  soils  is  with  a  few  exceptions  not  especi- 
ally rich  in  nitrogen,  and,  as  a  consequence,  the  soil  is  but 
meagerly  supplied. 


SOIL  COLUMNS  OF   THE   NORTHEASTERN  LAVA-BED   REGION 

The  lava-bed  region,  comprising  a  large  portion  of  the  north- 
eastern part  of  the  state,  reaches  north  from  the  Sierra  Nevada 
mountains  into  Oregon  and  is  a  region  of  lava-bed  plateaus  and 
hills  interspersed  with  occasional  valleys  that  are  capable  of 
cultivation  to  a  large  extent  in  grain,  some  fruits,  and  alfalfa. 

Honey  Lake  Valley.6 — This  valley  with  its  large  lake  lies 
between  the  foot  of  the  Sierras  and  the  lava  hills  on  the  north, 
and  has  an  elevation  of  about  4000  feet  above  sea-level.  It  is 
divided  into  the  Honey  Lake  Valley  proper  and  the  East  Side 
Valley,  which  extends  from  the  lake  eastward  into  the  desert 
region. 

Honey  Lake  occupies  the  greater  part  of  the  valley  and  is 
bordered  on  all  sides  by  lands  which  are  being  brought  under 
cultivation  in  grain  and  alfalfa,  except  on  the  east,  where  the 
soil  is  of  a  more  sandy  and  alkali  nature.  A  column  of  soil 
was  taken  to  a  depth  of  ten  feet  from  near  Standish  on  the  north 
side  of  the  valley;  a  large  and  luxuriant  growth  of  alfalfa 
covered  the  adjoining  fields. 


6  Described  by  Professor  Hilgard  in  Report  of  Agricultural  Experiment 
Station,  1891-92,  p.  24. 


242  Un  iuersity  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Another  column  of  soil,  taken  by  Professor  G.  W.  Shaw  from 
a  strong  alkali  tract  bordering  the  lake  on  the  east  side  near 
Amedee,  contained  but  0.25  per  cent  of  humus  in  the  first  and 
0.15  per  cent  in  the  second  foot  but  none  below  that  depth. 

East  Honey  Lake  Valley. — This  desert-like  region  comprises 
that  portion  of  Honey  Lake  Valley  in  Lassen  County  that  reaches 
eastward  from  the  lake  into  Nevada  at  an  elevation  of  about 
one  hundred  feet  more  than  the  lands  around  the  lake,  and  lies 
between  hills  of  lava  debris.  The  width  is  about  fifteen  miles,  but 
increases  much  more  toward  the  state  line.  The  soil  of  the  plain 
seems  to  be,  for  the  most  part,  quite  free  from  alkali  salts,  which 
appear  only  here  and  there  on  the  surface ;  but  toward  the  state 
line  at  lower  levels  the  alkali  is  more  abundant.  On  the  north 
side  of  this  plain  the  soil  is  quite  level  and  sandy,  with  a  reddish 
sandy  subsoil. 

A  wide  belt  of  alluvial  land  borders  Skedaddle  Creek  in  a 
depth  of  three  or  four  feet  near  the  creek.  Beneath  this  there 
is,  as  shown  in  a  well  on  the  place  of  A.  L.  Spoon  at  Stacy 
Station,  two  feet  of  sand  and  twenty  feet  of  a  calcareous  clay 
underlaid  in  turn  by  blue  sand  and  clay.  A  column  of  soil  was 
taken  for  examination  from  this  land  to  a  depth  of  twelve  feet. 

It  is  interesting  to  note  here  that  a  well  on  the  place  of  Mr. 
Caudle,  north  of  Stacy,  exposed  three  feet  of  a  reddish  soil,  three 
feet  of  sand,  seven  feet  of  boulders,  and  fifteen  feet  of  white 
calcareous  clay ;  below  this  appeared  blue  clay  to  a  depth  of 
320  feet  from  the  surface,  water  being  reached  at  that  depth. 

In  the  center  of  the  valley  the  surface  of  the  land  is  in  low 
ridges,  the  sandy  soil  being  blown  into  hillocks,  the  soil  being 
underlaid  by  a  very  compact  gray  silty  soil  to  ten  feet;  then 
beneath  that  is  ten  feet  of  a  fine  sand,  followed  by  ten  feet  of  a 
coarse  sand  in  which  water  is  struck  in  wells.  Beneath  this  lies  a 
blue  clay  of  fifty  feet  or  more  in  thickness.  A  column  of  soil 
was  taken  in  this  land  to  twelve  feet  depth,  four  miles  north  of 
Calneva.  On  the  south  of  the  Western  Pacific  Railroad  from 
Calneva  to  the  mountains  the  soil  is  coarsely  sandy. 

The  soil  of  Stacy  is  somewhat  remarkable  in  having  so  high 
a  percentage  of  humus  in  its  second  foot,  and  especially  in  having 
so  much  throughout  the  entire  column.     It  compares  well  with 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         243 


Table  38. — Humus  in  Soil  Columns  of  Honey  Lake  Valley,  Lassen  County 


East  Honey  Lake  Valley 


Honey  Lake  Valley 


Stacy 

North 

OF  Calxeva 

^ 

Stan  dish 

~t 

Soil 
Clav  11.29 
Ft. 

Humus 

Humus- 
Nitrogen  in 

Soil 
Clay  19.50 

Humus 

Humus- 
Nitrogen  in 

Soil 
Clay  14.58 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

Humus 

Soil 

Humus  Soil 

1   Dark  loam.... 

.64 

7.35 

.05 

Clay  loam  ... 

.       .25 

3.85 

.01 

Loam 

.72 

3.45      .03 

2   Dark  loam.... 

1.26 

4.68 

.06 

Clay  loam  ... 

.10 

tr. 

tr. 

Loam 

.33 

tr.       tr. 

3    Sandy 

.45 

6.22 

.03 

Clay  loam  ... 

.14 

Loam 

.17 

4   Sandy 

.47 

6.60 

.03 

Clay  loam  ... 

.       .17 

Whitish  loam 

.21 

5   Grittv 

.44 

7.05 

.03 

Clay  loam  ... 
Clay  loam  ... 

.13 

tr. 

6    Sandy 

.39 

6.40 

.03 

.13 

Whitish  loam 

7   Loam 

.34 

5.90 

.02 

Clay 

.       .12 

Whitish  loam 

8   Loam 

.27 

7.40 

.02 

Clav 

.       .10 

Whitish  loam 

.24 

8.32 

.02 

Clay 

Clay 

.16 

10   Loam 

.24 

7.08 

.02 

.       .15 

Whitish  loam 

11  Loam 

.22 

Sand 

.       .08 

Whitish  loam 

12    Loam 

.20 

Sand 

.       .07 

Whitish  loam 

Sum  of  per  cents 

5.16 

1.60 

1.43 

Average  per  foot 

.43 

6.70 

.03 

.13 

.13 

Upper  3  feet:* 

Sum  of  per  cents 

2.35 

.49 

1.22 

Average  per  foot 

.78 

6.08 

.05 

.16 

.41 

*  Range  of  most  annual  plant 

roots 

many  soils  of  the  more  favored  portions  of  the  state.  The  humus 
is  fairly  rich  in  nitrogen,  but  the  amount  given  to  the  soil  is 
small. 

The  soil  from  the  region  north  of  Calneva  contains  very 
little  humus  even  in  the  surface  foot,  but  it  is  found  throughout 
the  entire  column  and  is  very  poor  in  nitrogen.  The  humus  is 
apparently  derived  from  the  debris  and  roots  of  the  sagebrush 
and  alkali  weeds  that  grow  on  the  plain. 

With  an  abundant  water  supply  and  the  turning  under  and 
humification  of  some  good  legume  crop  there  is  no  reason  why 
the  lands  of  East  Honey  Lake  Valley  at  their  elevation  of  4000 
feet  above  sea-level  should  not  produce  crops  suitable  to  that 
altitude  as  well  as  the  lands  of  Imperial  Valley  which  are  below 
sea-level,  though  climatic  conditions  naturally  would  control  the 
kind  of  crops  grown. 

The  column  taken  from  an  alfalfa  field  near  Standish  on  the 
north  side  of  the  lake  is  surprisingly  low  in  humus  below  the 


244  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

surface  foot.  The  underlying  whitish  limy  loam  seems  to  have 
restricted  the  development  of  plant  roots  to  the  upper  four  feet. 
The  humus  is  also  poor  in  nitrogen  and  was  probably  derived 
from  the  meager  roots  of  sage  and  alkali  weeds. 

A  soil  previously  taken  from  the  Susanville  Meadows  had 
only  0.33  per  cent  of  humus,  and  another  from  two  miles  west  of 
Amedee  had  but  0.29  per  cent. 

Madaline  Plains. — Passing  north  from  Honey  Lake  Valley 
across  hills  covered  with  beds  of  lava,  we  come  to  the  Madaline 
Plains,  which  occupy  an  immense  and  almost  level  basin  (prob- 
ably once  an  inland  lake)  at  an  elevation  of  5200  feet  above  sea- 
level.  Its  area  is  approximately  150  square  miles,  very  irregular 
in  outline,  and  bordered  on  all  sides  by  lava  hills.  Its  soil  is 
a  dark  and  very  compact  clay,  underlaid  at  three  or  more  feet 
by  a  light-colored  marl  of  a  hardpan  nature  and  upwards  of 
seventy-five  feet  in  thickness,  as  shown  in  well-borings.  A  column 
of  this  soil  four  feet  in  depth  was  obtained  from  the  plain  to 
the  westward  of  the  place  of  W.  C.  Brockman.  Previous  analyses 
of  other  samples  show  fair  amounts  of  phosphoric  acid.  Grass 
and  grain  are  said  to  do  well  on  this  plain.  The  surface  foot  was 
found  to  contain  0.52  per  cent  of  humus,  and  the  second  foot 
0.60  per  cent,  but  below  this  the  clay  was  almost  free  from  it. 
The  soil  contains  about  0.04  per  cent  of  humus-nitrogen. 

Pitt  River  Valley. — Pitt  River,  with  its  source  at  the  western 
foot  of  the  Warner  range  of  mountains,  passes  through  a  number 
of  valleys  as  it  flows  westward  into  the  Sacramento  River.  The 
town  of  Alturas  is  located  in  one  of  these  valleys  at  the  junction 
of  the  two  forks  of  the  river.  The  soil  of  the  valley  is  chiefly 
meadowland  with  water  at  a  depth  of  a  few  feet  and  partly 
grown  in  tules,  but  affording  large  alfalfa  tracts.  A  column  of 
six  feet  was  taken  from  an  alfalfa  field  near  the  town.  The 
valley  is  bordered  by  lava-beds  and  hills.  Goose  Lake  Valley  to 
northward  and  reaching  into  Oregon  has  a  similar  meadowland 
soil  reaching  from  the  lake  eastward  to  the  foot  of  the  mountains, 
where  the  disintegrated  debris  affords  some  higher  land  on  which 
orchards  are  planted. 

Klamath  Lake  Marshes. — A  column  from  the  frule  marshes  of 
Klamath  Lake,  Butte  Valley,  was  obtained  for  us  by  Mr.  L.  S. 
Robinson  for  examination. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         24.3 

Table  39.— Humus  in  Soil  Columns  of  Pitt  River  and  Butte  Valleys 

Pitt  River  Valley  Butte  Valley 

MODOC  COUNTY  SISKIYOU   COUNTY 

Alturas  Klamath 

Humus-  Humus- 
Soil                                 Nitrogen  in  Soil                                 Nitrogen  in 

Clay  29.60  , -*- *  Clay  11.00  , * , 

Ft.                           Humus    Humus  Soil  Humus    Humus  Soil 

1  Clay 3.05           1.93      .06  Marsh  loam..     3.75          9.15      .34 

2  Clay 1.45          3.39      .05  Marsh  loam..     3.20          7.10      .23 

3  Clay 1.01          5.85      .06  Marsh  loam..     3.02          9.07      .27 

4  Clay 87          3.22      .03  Marsh  loam..     2.84          8.88      .25 

5  Clay 51           1.09      .01  Ashy  loamt  -      .91           7.70      .07 

6  Clay 34          1.65      .01  Ashy  loamy  -      .74          7.58      .06 

7  Water Dark  clay 06  

8  Dark  clay  ....        tr.  

Sum  of  per  cents     7.23  14.52 

Average  per  foot     1.20          2.85      .03  1.81           8.25      .20 

Upper  3  feet  :* 

Sum  of  per  cents    5.51  9.97 

Average  per  foot     1.84          3.72      .06  3.32           8.44      .28 

*  Range  of  most  annual  plant  roots. 
t  Infusorial  earth. 


Both  of  the  above  soils  are  rich  in  humus,  though  differing 
greatly  in  other  respects.  The  Alturas  is  a  clay  soil  under  culti- 
vation in  alfalfa,  and  while  its  humus  is  poor  in  nitrogen  the 
amount  given  to  the  soil  is  fair.  On  the  other  hand,  the  Klamath 
column  is  from  tule-marsh  lands,  containing  a  larger  proportion 
of  decaying  vegetable  matter,  and  consequently  is  quite  rich  in 
humus.  The  latter  is  especially  rich  in  nitrogen  and  as  a  con- 
sequence the  soil  is  also  well  supplied  in  nitrogen  through  its 
upper  four  feet.  The  fifth  and  sixth  foot  are  largely  made  up  of 
diatomaceous  earth  in  which  the  humus  has  suddenly  diminished 
to  less  than  1  per  cent. 

Surprise  Valley. — Eastward  from  Alturas,  the  Warner  range 
of  mountains  separates  the  Pitt  River  Valley  from  Surprise 
Valley  with  its  three  large  lakes.  The  land  of  the  eastern  side 
of  this  valley  is  strongly  charged  with  alkali  salts,  but  on  the 
west  the  broad  slope  from  the  mountains  to  the  lake  presents 
excellent  agricultural  capabilities,  the  production  of  alfalfa  seed 
being  quite  a  prominent  industry.    A  column  of  soil  ten  feet  deep 


246  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

(to  water)  was  obtained  two  miles  south  of  Cedarville  with  the 
assistance  of  Mr.  W.  L.  Turner,  and  another  column  of  four  feet 
from  the  meadowland  that  forms  a  broad  border  to  the  lake,  and 
in  which  water  was  struck  at  four  feet, 


Table  40. — Humus  in  Soil  Columns  of  Surprise  Valley,  Modoc  County 

Cedarville  Cedarville 

Humus-  Humus- 
Soil                                Nitrogen  in  Soil                               Nitrogen  in 

Clay  10.97  , -*- N  , -X        ^ 

Ft,                           Humus    Humus  Soil  Ft,                           Humus    Humus  Soil 

1  Loam 4.27  1.14  .05  Meadow  loam    2.71  3.46      .09 

2  Loam 1.25  3.36  .04  Meadow  loam    2.10  4.62      .10 

3  Loam 1.21  2.81  .03  Meadow  loam      .86  8.02      .07 

4  Loam 93  2.26  .02  Meadow  loam      .79  7.59      .06 

5  Loam 64  2.66  .02  Water     

6  Loam 63  2.67  .02 

7  Loam 56  3.93  .02 

8  Loam 60  2.33  .01 

9  Loam 51  2.55  .01 

10   Loam 36  4.72  .02 

Sum  of  per  cents  10.96  6.46 

Average  per  foot     1.10  2.84      .03  1.62  5.92      .08 

Upper  3  feet :  * 
Sum  of  per  cents     6.73  5.67 

Average  per  foot     2.25  2.44      .04  1.89  5.37      .09 

*  Range  of  most  annual  plant  roots. 


The  surface  soil  of  the  Cedarville  loam  is  surpassed  in  its 
percentage  of  humus  only  by  the  black  clay  of  Santa  Clara  and 
the  marsh  lands  among  all  of  the  soils  of  the  'state  thus  far 
examined,  and  it  ranks  fifth  with  regard  to  the  amount  in  the 
three  upper  feet.  The  percentage  throughout  the  entire  column 
of  ten  feet  is  quite  high.  This  high  humus  content  may  be  due 
to  the  alfalfa  crops  that  have  been  produced  for  seed  on  this 
soil  for  a  number  of  years  past,  as  a  soil  from  another  locality 
near  Cedarville  examined  ten  years  ago  contained  but  1.56  per 
cenl  in  the  surface  foot.  The  humus  is,  however,  remarkably 
weak  in  uitrogen,  if  such  was  its  origin. 

The  meadow  soil  lying  al  n  lower  level  is  very  similar  to  that 
of  Alturas  in   its  humus  content. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         247 

SOIL   COLUMNS  OF   THE  " DESERT"   PLAINS 

The  term  ''desert"  is  here  applied  to  the  extent  of  country 
with  scant  rainfall  and  having  a  vegetation  of  sagebrush  and 
largely  devoid  of  grasses;  a  country  whose  soils  are  usually  rich 
in  the  mineral  elements  of  plant  food  and  which  are  remarkable 
for  their  fertility  when  properly  cultivated  and  abundantly 
irrigated.  The  reason  for  this  fertility  lies  partly  in  the  fact 
that  the  humus,  though  small  in  amount,  is  with  its  nitrogen  well 
distributed  throughout  a  depth  of  twelve  feet  and  more,  in  a  soil 
whose  sandy  or  silty  texture  permits  deep  rooting  of  plants. 

The  desert  lands  are  interspersed  with  mountain  ranges 
separated  by  valleys  of  greater  or  lesser  extent.  Some  of  these 
valleys  have  with  irrigation  been  brought  under  cultivation  and 
settlement  and  from  these  a  few  soil  columns  were  secured. 

Imperial  Valley. — This  newly  settled  part  of  the  state,  once 
the  bed  of  Salton  basin  which  on  drying-up  became  a  desert 
until  reclaimed  by  irrigation,  largely  lies  below  the  level  of  the 
sea.     Its  soils,  derived  from  the  sediment  of  the  Colorado  River, 


Table  41. — Humus  in  Soil  Columns  of  Imperial  Valley, 
Imperial  County 


Imperial 

El 

Centro 

Soil 
Clay  50.43 
Ft.                           Humus 

Humus- 
Nitrogen  in 

Soil 
Clay  47.42 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

Humus 

Soil 

1    Silty  clay 

.26 

6.14 

.02 

Silty  clay...... 

.   .     30 

5.15 

.02 

2   Silty  clay 

.24 

3.51 

.01 

Silty  clay 

.       .23 

5.49 

.01 

3    Silty  clay 

.21 

3.34 

.01 

Clay 

.       .22 

6.38 

.01 

4   Clay 

.19 

4.43 

.01 

Clay 

.       .21 

4.54 

.01 

5    Silt 

.17 

6.61 

.01 

Clay 

.      .32 

4.39 

.01 

6   Silt 

.21 

4.01 

.01 

Clay 

.       .27 

5.20 

.01 

7   Clay 

.22 

3.83 

.01 

Clay 

.       .26 

4.86 

.01 

8   Clay 

.15 

4.68 

.01 

Clay 

.       .31 

4.08 

.01 

9    Silt 

.14 

4.01 

.01 

Clay 

.       .28 

5.01 

.01 

10   Silt 

.13 

5.40 

.01 

Clay 

.       .32 

3.51 

.01 

11    Silt 

.10 

8.42 

.01 

Clay 

.       .29 

2.91 

.01 

12   Clay 

.14 

4.01 

.01 

Clay 

.       .20 

5.62 

.01 

Sum  of  per  cents 

2.16 

3.21 

Average  per  foot 

.18 

4.86 

.01 

.27 

4.76 

.01 

Upper  3  feet :  * 

Sum  of  per  cents 

.71 

.75 

Average  per  foot 

.24 

4.33 

.01 

.25 

5.67 

.01 

Range  of  most  annual  plant  roots. 


248  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

have  a  peculiar  light  pinkish  tint  and  are  made  up  of  alternating 
strata  of  silt  and  a  very  plastic  and  impervious  clay  of  varying 
thicknesses.  When  this  clay  forms  the  surface  soil,  the  difficulties 
of  cultivation  and  irrigation  are  very  great;  but  if  the  clay  lies 
at  a  depth  of  several  feet  below  the  surface  of  a  silty  soil  then 
the  reverse  is  true.  This  peculiar  type  of  land  is  represented  in 
the  series  by  two  columns  of  soil,  one  from  the  vicinity  of 
Imperial  and  the  other  from  near  El  Centro ;  these  and  that  from 
Coachella  were  taken  by  Mr.  F.  E.  Johnson. 

Mojave  River  Mesa. — The  mesa  or  plain  is  formed  by  accumu- 
lation of  granitic  debris  from  the  Sierra  Madre  Mountains  on 
the  south  and  reaches  far  out  toward  Barstow,  San  Bernardino 
County.  This  debris  is  coarse  and  quite  compact,  and  in  the 
neighborhood  of  Victorville  is  said  to  have  a  thickness  of  thirty- 
five  feet  or  more.  It  is  here  overlaid  by  about  three  feet  of  a 
gray  sandy  soil,  also  quite  compact  and  supporting  a  sparse 
vegetation  of  weeds.  A  column  of  eleven  feet  was  obtained  three 
miles  west  of  Victorville.  The  soil  was  found  to  contain  but 
0.13  per  cent  of  humus  in  the  surface  foot,  0.14  per  cent  in  the 
second,  0.10  per  cent  in  the  third,  and  0.08  per  cent  in  the  coarse 
sand  of  the  fourth  foot.  There  were  but  traces  of  nitrogen  in 
the  humus.    The  soil  has  11.05  per  cent  of  clay. 

Coachella  Valley. — A  column  was  obtained  from  the  vicinity 
of  Coachella  and  represents  the  higher  and  more  sandy  lands 
that  bordered  the  old  Salton  Lake  of  the  Imperial  country. 

Owens  River  Valley. — The  agricultural  lands  of  this  valley 
lie  chiefly  on  the  west  side  of  Owens  River  and  are  formed  of 
the  debris  of  the  adjoining  Sierra  Nevada.  A  column  of  soil  was 
secured  through  the  kindness  of  Mr.  W.  K.  Winterhalter  of  San 
Francisco. 

It  was  to  be  anticipated  that  the  soils  of  what  are  known  as 
the  desert  plains  of  the  eastern  and  southeastern  part  of  the 
state  would  be  very  poor  in  humus  because  of  their  very  sandy 
nature,  together  with  small  rainfall,  extreme  summer  heat  and 
scant  vegetation,  but  it  was  a  surprise  to  find  that  humus  occurred 
at  depths  of  twelve  or  more  feet  below  the  surface.  The  soil 
poorest  in  humus  is  that  from  the  mesa  plain  just  west  of 
Victorville,  in  which  plant  roots  were  found  in  a  depth  of  three 
feel   only,  the  underlying  materia]  being  too  compact  for  root 


1914]       Lougliridge:  Humus  and  Xitrogen  in  California  Soil  Columns  249 


Table  42. — Humus  in  Soil  Columns  of  Other  Valleys 


COA' 

CHEL] 

LA   VA 

LLEY 

ChvENS  Valley 

RIVERSIDE    COUNTY 

INYO  COUNTY 

COACHELLA 

Bishop 

Soil 
Clay  16.90 
Ft.                           Humus 

Humus- 
Nitrogen  in 

Soil 
Clay  6.28 

Humus 

Humus- 
Nitrogen  in 

Humus 

Soil 

Humus  Soil 

1   Loam.... 

.32 

5.27 

.01 

Sandy 

31 

3.55      .01 

2    Loam.... 

.22 

5.74 

.01 

Sandy 

23 

3    Loam 

.14 

6.02 

.01 

Sandy 

19 

4   Loam.... 

.13 

1.08 

tr. 

Sandy 

19 

5   Loam 

.10 

1.40 

tr. 

Sandy 

13 

.14 
.11 

4.01 
5.11 

.01 
.01 

Sandy 

Sandy 

07 

08 

7   Loam 

8   Loam.... 

.14 

4.01 

.01 

Sandy  

08 

9   Loam.... 

.12 

4.68 

.01 

Sandy 

08 

10   Loam 

.15 

5.62 

.01 

Sandy 

06 

11   Loam.... 

.16 

6.14 

.01 

Sandy 

08 

12   Loam.... 

.13 

4.32 

.01 

Sandy 

06 

Sum  of  per  < 

?ents 

1.86 

1.56 

Average  per 

foot 

.15 

4.45 

.01 

.13 

Upper  3  feet  :* 

Sum  of  per  cents 

.68 

.73 

Average  per 

foot 

.23 

5.68 

.01 

.24 

Range  of  most  annual  plant  roots. 


penetration.  It,  however,  supported  a  growth  of  yueca  and 
desert  weeds,  and  on  the  same  mesa,  near  Hesperia,  with  pre- 
sumably the  same  soil  though  deeper,  there  are  a  few  orchards. 
A  glance  at  the  table  shows  that  there  is  nearly  the  same  per- 
centage of  humus  in  the  first  foot  of  each  of  the  columns  and 
very  little  difference  in  the  total  amount  in  the  upper  three  feet. 
The  very  unequal  distribution  in  the  El  Centro  column  is 
somewhat  surprising,  for  it  might  readily  be  supposed  that  the 
small  amount  in  the  surface  foot  would  indicate  that  there  was 
scarcely  any  in  the  lower  depths;  whereas  we  find  higher  per- 
centages in  the  fourth,  fifth,  eighth,  and  tenth  foot  respectively 
than  in  either  of  the  upper  three  feet.  It  is  interesting  to  note 
that  there  is  more  in  the  lower  half  of  the  column  than  in  the 
upper.  The  humus  of  these  columns  is  not  quite  as  rich  in 
nitrogen  as  are  the  soils  from  other  parts  of  the  state,  and  that 
of  the  Bishop  column  is  extremely  low.  The  nitrogen  of  the  soil 
is  not  more  than  0.01  per  cent,  or  about  400  pounds  per  acre-foot. 


250  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 


GENERAL  SUMMARY 

INDIVIDUAL    SOIL    COLUMNS    HAVING    THE    HIGHEST 
HUMUS  CONTENT 

In  looking  over  the  109  columns  of  soil  taken  from  the  various 
agricultural  regions  of  the  state,  we  find  that  eighteen  have  each 
more  than  2  per  cent  of  humus  in  the  surface  foot,  and  thirty- 
two  others  have  more  than  1  per  cent,  the  remaining  fifty-nine 
having  less  than  that. 

The  following  twenty-five  localities  are  worthy  of  special 
mention,  for  in  their  respective  columns  more  than  1  per  cent 
of  humus  is  found  in  each  individual  soil  layer  to  depths  of 
three  to  seven  and  even  nine  feet  below  the  surface;  they  are 
ranged  according  to  depth. 

Table  43. — Columns  with  1  per  cent  of  Humus  in  Three  or  More 
Individual  Feet 

Soil  Locality  County  Depth 

Tule Stockton  San  Joaquin  9  ft. 

Loam Arroyo  Grande  Valley  San  Luis  Obispo 7  ft. 

Loam Arroyo  Grande  Seed-farm  ....San  Luis  Obispo 7  ft. 

Clay  loam Lompoc  Seed-farm  Santa  Barbara   7  ft. 

Loam iSanta  Rosa  Sonoma  6  ft. 

Adobe Berkeley Alameda  6  ft. 

Loam Russian  River  Sonoma  5  ft. 

Clay  loam Walnut  Creek  Contra  Costa  5  ft. 

Adobe El  Verano  Sonoma  4  ft. 

Loam ^Yountville   Napa   4  ft. 

Clay Gilroy  „..Santa  Clara  4  ft. 

Loam Chino    San    Bernardino    4  ft. 

Loam Klamath  (tule)  Siskiyou   4  ft. 

Loam Glenn    Glenn  3  ft. 

Sandy Chico    Butte  3  ft. 

Clay  loam Davis  Yolo  3  ft. 

Clay Farmington  San  Joaquin  3  ft. 

Loam Newcastle    Placer   3  ft. 

Loam Kenwood    Sonoma  3  ft. 

Adobe San  Ramon  Contra  Costa  3  ft. 

Clay Santa  Clara  Seed-farm  Santa  Clara  3  ft. 

Loam Pomona  Cienega ..Los  Angeles  3  ft. 

Clay Santa  Ana  Orange    3  ft. 

Clay Alturas    meadow    Modoc   3  ft. 

Loam Cedarville Modoc   3  ft. 


1914]       Loughridge :  Humus  and  Nitrogen  in  California  Soil  Columns         251 

A  number  of  other  localities  very  nearly  come  into  the  list 
as  their  upper  two  feet  have  more  than  1  per  cent  and  the  third 
falls  a  little  below.  It  will  be  noted  that  these  results  are  not 
confined  to  any  particular  soil  type  but  that  all  types  from  sandy 
to  heavy  clay  adobe  are  represented  in  the  list. 

If  the  humus  of  the  upper  three  feet  be  equally  distributed 
through  that  depth  we  will  find  that  nine  of  the  columns 
have  each  an  average  of  more  than  2  per  cent  of  humus  in 


Table  44. — Soil  Columns  Having  the  Highest  Humus  Percentages 


Average  of  Upper 

Three 

Average  of  Entire  Column 

In  First  Foot 

Feet 

of  10  or  12  Feet 

Per  cent 

Per  cent 

Per  cent 

Stockton  tule  

..  14.10 

Stockton  tule  

...  16.68 

Stockton  tule  

6.81 

Pomona  Cienega  

..     6.26 

Pomona  Cienega  

...     3.67 

Arroyo   Grande   

1.39 

Santa  Clara  adobe.... 

..     4.43 

Santa  Clara  adobe... 

...     3.63 

Santa  Clara   (10  feet) 

1.33 

Cedarville  

..     4.29 

Klamath  marsh  

...     3.32 

Pomona  Cienega  

1.28 

Arroyo  Grande  seed- 

Arroyo  Grande  seed- 

farm  

..     3.78 

Cedarville  

...     2.25 

farm  

1.27 

Klamath  marsh  

..     3.75 

Gilroy    

...     2.23 

Gilroy    

1.14 

Alturas  meadows  

..     3.05 

Arroyo  Grande 

Arroyo  Grande  seed 

...     2.16 

Cedarville  (10  feet).... 

1.10 

Gilroy    

..     2.76 

farm  

...     2.15 

Lompoc  seed-farm 

1.09 

Cedarville  meadows.. 

..     2.71 

Berkeley  adobe  

...     2.01 

Berkeley  

1.04 

Yountville    

..     2.64 

Yountville    

...     1.98 

Russian  River  

1  01 

Lompoc  seed-farm  .... 

..     2.50 

Cedarville  meadows. 

...     1.89 

Yountville    

.95 

Arroyo  Grande 

..     2.50 

Lompoc  seed-farm  ... 

...     1.86 

Santa  Rosa  

.92 

Santa  Ana  adobe 

..     2.42 

Alturas  meadow  

...     1.84 

El  Yerano  (10  feet).... 

1.00 

Chino  moist  land  

..     2.31 

Kenwood  

...     1.74 

Walnut  Creek  

,80 

Kenwood  

..     2.25 

El  Verano  adobe  

...     1.71 

Hayward  

.77 

El  Verano  adobe 

..     2.14 
2.13 

Farmington    

...     1.65 
1.63 

Davis  Univ.  Farm 

Watsonville    . 

.75 

Berkeley  adobe 

Farmington 

Santa  Ana  adobe 

.74 

..     2.04 

Russian  River  

...     1.58 

Chico   

.73 

Vacaville 

..     1.97 
..     1.95 

Chino  

...     1.52 
...     1.51 

Vacaville  

Glenn  

71 

Santa  Rosa  

Glenn  

.69 

the  upper  three  feet,  and  twenty-five  others  have  an  average 
of  more  than  1  per  cent,  all  others  falling  below  the  1  per  cent. 
In  the  distribution  of  the  humus  through  the  entire  twelve  feet 
of  the  columns  there  are  ten  which  thus  give  an  average  of  more 
than  1  per  cent  for  each  foot,  and  twenty-five  others  whose 
average  is  about  one-half  of  1  per  cent. 


252  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

In  the  following  table  we  have  placed  the  names  of  the  twenty 
localities  which  have  as  much  as  1.95  per  cent  in  the  surface 
foot,  and  the  twenty  which  rank  highest  in  averages  of  the  upper 
three  feet  and  in  the  entire  column  of  ten  or  twelve  feet. 


Composite  Columns  of  Agricultural  Regions 

In  the  following  table  are  given  the  averages  of  each  of  the 
agricultural  regions  embracing  all  of  the  109  columns  represent- 
ing the  state  at  large,  taken  from  thirty-seven  counties.  The  tule 
marshes  of  Stockton,  Pomona,  and  Klamath  are  placed  in  a 
column  by  themselves.  In  some  of  the  individual  columns  that 
form  the  composite  for  each  region  either  a  depth  of  twelve  feet 
was  not  secured  or  the  humus  itself  was  not  found  to  that  depth. 

The  marsh  lands  are  naturally  richest  in  humus  because  of 
the  large  amount  of  decaying  vegetable  matter  they  hold.  But 
next  to  these  we  find  that  the  Coast  Range  valleys  have  the 
highest  amount  in  the  surface  foot,  the  upper  three  feet,  and  in 
the  entire  column  respectively.  The  lava-bed  valley  and  meadow 
lands  are  but  little  above  the  Sacramento  Valley  in  amount  of 
humus,  while  the  San  Joaquin  Valley  falls  behind  Southern 
California.  The  "desert"  plains  naturally  are  lowest  of  the 
eight  groups,  but  it  is  interesting  to  note  that  in  the  quite  even 
distribution  throughout  the  column  there  is  a  larger  amount  in 
the  lower  six  feet  than  is  found  in  the  lower  six  feet  of  either 
the  San  Joaquin  Valley  or  the  lava-bed  valleys. 

In  the  foothill  and  lava-bed  valleys  the  upper  two  feet  hold 
one-half  of  the  total  humus;  in  the  desert  lands  one-half  of  the 
humus  is  distributed  through  the  upper  five  feet  of  soil,  while  in 
each  of  the  other  columns  the  upper  three  feet  holds  one-half  of 
the  humus. 

The  first  foot  of  the  desert  lands  contains  but  about  one-eighth 
of  the  total  amount  of  humus  of  the  column;  that  of  the  Coast 
Range  valleys  and  the  marshes,  a  little  more  than  one-fifth ;  while 
in  the  other  regions  the  upper  foot  holds  from  one-third  to  one- 
fourth  of  the  total  amount  found  in  the  respective  columns. 

On  glancing  at  the  table  the  attention  is  first  called  to  the 
depth  of  twelve  feet  to  which  humus  reaches  in  all  of  the  com- 


1914]       Loughridge:  Humus  and  Nitrogen  in  Calif ornia  Soil  Columns         253 
Table  45. — Composite  Averages  of  Agricultural  Regions  (in  percentages) 


Sacra- 
mento 
Valley 

San 

Joaquin 

Valley 

Coast 
Range 
Valleys 

Southern 
Cali- 
fornia 

Sierra 
Nevada 
Foothills 

N.E.  Lava 

Beds      "Desert" 
Valleys      Plains 

Tule 
Marshes 

Depth 

18 
columns 

23 
columns 

24 
columns 

25 
columns 

3 

columns 

8 
columns 

5 

columns 

3 

columns 

1st    ft... 

1.04 

.80 

1.94 

.88 

1.12 

1.55 

.26 

8.04 

2nd  ft.  - 

75 
.58 

.51 
.37 

1.47 
1.13 

.65 
.45 

.71 
.57 

.92 
.48 

.19 
.17 

8.59 

3rd  ft.  .. 

7.05 

4th   ft.  .. 

.45 

.25 

.93 

.37 

.39 

.40 

.25 

5.52 

5th  ft.  .. 

.36 
.32 

.23 

.17 

.67 

.31 
.27 

.18 
.14 

.21 
.18 

.18 
.13 

2.65 

6th  ft... 

1.45 

7th  ft.  .. 

.23 

.14 

.59 

.25 

.18 

.13 

.13 

.78 

Sth  ft.  .. 

.19 

.10 

.49 

.19 

.10 

.12 

.14 

1.64 

9th   ft.  .. 

.18 

.18 

.41 

.16 

.11 

.12 

.68 

10th  ft... 

.17 

.06 

.39 

.16 

.09 

.13 

.30 

11th  ft.  .. 

.16 

.06 

.27 

.13 

.03 

.15 

.21 

12th  ft... 

.15 

.04 

.32 

.11 

.03 

.13 

.29 

In  1-2  feet 

Sum  of  humus  per 

cents   .. 

4.5  S 

2.91 

9.38 

3.93 

3.39 

4.25 

1.98 

37.20 

Nitrogen 

in 

humus 

5.45 

6.53 

5.15 

5.54 

5.64 

3.69 

4.69 

5.63 

Xitrogen 

in 

soil.... 

.03 

.02 

.04 

.02 

.03 

.03 

.01 

.02 

In  upper  3  feet* 
Sum  of  humus  per 


cents  

2.37 

1.6S 

4.54 

1.98 

2.40 

2.95 

.62 

23.68 

Xitrogen  in  humus 

5.79 

6.27 

5.13 

5.74 

5.40 

3.79 

4.97 

5.75 

Xitrogen  in  soil.... 

.04 

.04 

.07 

.03 

.05 

.05 

.01 

.44 

In  surface  foot 

Xitrogen  in  humus 

5.6S 

6.08 

5.43 

6.50 

5.93 

3.53 

5.03 

6.35 

Xitrogen  in  soil.... 

.05 

.05 

.10 

.05 

.07 

.05 

.02 

.47 

Range  of  most  annual  plant  roots. 


posite  columns  except  that  of  the  Sierra  Nevada  foothills,  the 
lava-bed  meadows  and  the  tule  marshes,  where,  because  of  the 
underlying  country-rock  on  the  one  hand  and  of  water  on  the 
other,  the  depths  are  limited  to  eight,  ten  and  seven  feet  respec- 
tively. Seventy-five  of  the  columns  have  a  depth  of  twelve  : 
eleven  others  a  depth  of  ten  feet,  and  eight  a  depth  of  nine  : 
In  some  of  the  columns  the  amount  of  humus  is  so  high  in  the 
twelfth  foot,  especially  in  that  of  the  valleys  of  the  Coast  Range. 
as  to  leave  no  doubt  of  its  being  found  at  a  greater  depth  had 


254  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

the  examination  been  made.  In  fact,  the  column  of  Fort  Romie 
was  carried  through  fifteen  feet,  and  0.41  per  cent  of  humus 
with  6.83  per  cent  of  nitrogen  was  found  in  the  lowest  foot. 

The  next  point  of  interest  is  the  small  amount  of  humus  in 
the  first  foot  of  each  of  the  columns  excepting  those  of  the 
meadowlands  and  the  tule  marshes.  This  is  especially  noticeable 
in  the  composite  of  the  San  Joaquin  Valley  and  in  that  of  the 
"desert"  plains.  The  general  average  of  the  surface  foot  for  all 
of  the  columns,  excluding  the  marshes,  is  1.16  per  cent. 

Another  point  of  special  interest  is  the  gradual  diminution 
of  humus  percentage  downward  in  each  of  the  composite  columns 
with  an  occasional  slight  increase,  as  is  seen  in  the  eleventh  foot 
of  the  Sacramento  Valley'  and  in  the  twelfth  foot  of  the  Coast 
Range  valleys.  This  decrease  indicates  smaller  amounts  of 
humus-forming  vegetable  material,  presumably  the  roots  of 
plants,  in  each  successive  foot  downwards,  the  main  mass  of  the 
root  systems  being  in  the  upper  three  or  four  feet. 

Averages  of  Three  Upper  Feet. — A  depth  of  one  foot  in  Cali- 
fornia does  not  in  reality  represent  the  soil  which  is  at  least  three 
feet  deep,  and  it  would  not  be  correct  or  fair  to  the  cultural 
possibilities  of  the  land  to  draw  conclusions  from  the  humus  of 
the  first  foot  alone.  It  is  very  true  that  its  presence  to  the 
extent  of  several  per  cent  near  the  surface  is  of  special  import- 
ance in  maintaining  proper  physical  textural  conditions  for 
aeration,  avoidance  of  crusts  and  easy  penetration  of  water,  but 
it  is  of  as  great  importance  that  there  should  be  several  per  cent 
of  humus  in  each  of  the  upper  several  feet;  for  in  arid  regions 
it  is  below  the  first  foot  and  away  from  hot  and  dry  soil  that 
the  feeding  roots  of  plants  prefer  to  carry  on  their  activities, 
and  it  is  in  the  upper  three  feet  that  the  main  mass  of  fine 
feeding  roots  are  usually  located,  and  where  they  must  secure 
the  needed  plant  food  supplied  by  the  humus.  This  not  only 
protects  the  roots  but  gives  to  them  a  far  greater  feeding  area 
which  is  enlarged  with  the  extension  of  the  humus  downward. 
The  summations  for  three  feet  are  given  at  the  foot  of  the  table. 

Sacramento  Valley. — This  valley,  represented  in  the  above 
table  by  a  composite  column  of  eighteen  individual  columns,  is 
nol  only  richer  than  the  San  Joaquin  Valley  in  the  first  foot  in 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         255 

humus,  but  in  every  foot  of  the  entire  column  to  a  depth  of 
twelve  feet.  One  half  of  the  total  amount  is  held  in  the  upper 
three  feet.  Its  first  foot  contains  a  little  less  than  that  of  the 
Southern  California  column,  but  in  the  upper  three  feet  and  in 
the  entire  column  there  is  more.  The  percentage  in  the  first  foot 
is  too  small  and  clearly  shows  the  need  of  being  increased  by  a 
system  of  growing  and  turning  under  of  green  crops.  With  this 
to  encourage  the  growth  of  the  young  grain  and  trees,  the 
lower  portion  of  the  column  will  afford  humus-nitrogen  and  other 
plant  food  for  the  roots  that  find  their  way  downward  to  twelve 
or  more  feet  as  was  the  case  with  wheat  and  barley  roots  on  the 
University  Farm  at  Davis.  In  the  latter  soil  the  humus  of  the 
first  foot  was  only  0.85  per  cent  and  that  of  the  second  foot 
1.49  per  cent,  and  the  ordinary  yield  had  been  but  from  twelve 
to  fourteen  bushels  of  wheat  per  acre  before  the  University 
bought  the  property.  By  proper  methods  of  treatment  and 
without  irrigation  or  fertilization  the  agronomist  in  charge, 
Professor  G.  W.  Shaw,  secured  a  yield  of  40.4  bushels  of  wheat 
per  acre  as  an  average  of  three  years,  during  which  time  the 
average  for  the  state  was  but  14.5  bushels.7 

The  humus-nitrogen  content  of  the  upper  three  feet  of  the 
Sacramento  composite  column  is  5.79  per  cent  of  the  humus  which 
thus  gives  0.04  per  cent  to  the  soil.  This  is  approximately  1600 
pounds  of  nitrogen  per  acre  for  each  foot  in  depth. 

San  Joaquin  Valley. — The  composite  of  twenty-three  columns 
from  the  San  Joaquin  Valley  shows  humus  percentages  much 
below  those  of  other  regions,  both  in  the  surface  foot  (0.80  per 
cent)  and  in  each  foot  of  the  entire  column.  The  sum  of  3.11 
per  cent,  if  contained  in  the  upper  foot  of  the  three  feet,  would 
be  a  fair  amount,  though  much  below  that  of  other  regions.  The 
low  percentages  may  be  due  in  part  to  the  presence  of  alkali 
salts  in  some  of  the  soils  examined,  also  to  a  more  arid  climate 
of  far  less  rainfall  than  in  other  regions,  and  to  a  less  luxuriant 
vegetation  upon  the  decay  of  whose  roots  the  amount  of  humus 
is  dependent. 

Although  this  humus  percentage  is  so  low  in  the  upper  part 
of  the  soil,  yet  a  proper  system  of  deep  plowing  to  break  up  any 


7  Bull.  no.  211,  Cal.  Agr.  Expt.  Sta. 


256  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

tendency  to  form  a  plowsole  and  to  make  the  soil  loose  and  of 
good  texture  for  a  downward  development  of  the  grain  roots, 
which  may  thus  secure  the  benefits  of  the  humus,  would  tend 
greatly  to  increase  the  grain  jdelds  of  the  valley.  This  was  shown 
in  the  experiments  of  Professor  G.  W.  Shaw  at  Ceres  and  Tulare,8 
where  during  a  period  of  three  years  by  this  method  the  average 
yield  of  wheat  was  thirty-five  and  thirty-three  bushels  respec- 
tively, during  which  period  the  average  wheat  for  the  state  was 
14:. 5  bushes  per  acre.  No  irrigation  or  fertilization  was  used  in 
his  experiments. 

The  humus-nitrogen  of  the  upper  three  feet  of  the  composite 
column  is  6.27  per  cent  of  the  humus,  which  is  higher  than  in 
any  of  the  other  composite  columns  in  the  table.  In  the  soil 
itself,  however,  there  is  but  an  average  of  0.04  per  cent,  or  1600 
pounds  per  acre-foot. 

Sierra  Nevada  Foothills. — The  composite  of  three  columns 
from  the  Sierra  Nevada  foothills  shows  more  humus  in  the  first 
foot  than  in  that  of  the  Sacramento  Valley  or  Southern  Cali- 
fornia. That  of  the  second  foot  is,  however,  somewhat  less,  and 
there  is  a  greater  decrease  in  the  lower  part  of  the  column,  the 
sum  being  but  3.39  per  cent  in  the  eight  feet.  More  than  one- 
half  of  the  humus  is  held  in  the  upper  three  feet. 

The  humus-nitrogen  in  the  upper  three  feet  of  the  composite 
column  is  5.4  per  cent  of  the  humus,  or  0.05  per  cent  in  the  soil, 
and  is  equivalent  to  2000  pounds  for  each  acre-foot  in  the  three 
feet. 

Coast  Range  Valleys. — The  composite  column  of  the  twenty- 
four  soils  of  the  valleys  of  the  Coast  Range  shows  a  general 
average  of  nearly  2  per  cent  of  humus  in  the  surface  foot  and  thus 
is  far  above  each  of  the  other  columns,  except  the  marshes  and 
meadowlands.  Not  only  that,  but  it  is  the  only  composite  column 
of  the  uplands  which  has  more  than  1  per  cent  in  the  subsoils 
immediately  below  the  first  foot.  The  percentage  of  humus  in 
each  of  the  succeeding  feet  throughout  the  twelve  feet  is  also 
higher  than  in  any  other  of  the  composite  columns;  the  twelfth 
fool  has  nearly  one-half  of  1  per  cent  and  the  sum  of  the  entire 
column   is  9.38  per  cent.     The  humus  is  not  as  rich  in  nitrogen 


BBull.  No.  211,  Calif.  Agr.  Exp.  Sta. 


1914]       Loughridge:  Humus  and  Nitrogen  in  Calif  ornia  Soil  Columns         257 

as  that  of  the  San  Joaquin  or  Southern  California,  and  the 
amount  of  organic  nitrogen  in  the  soil  is  below  the  0.05  per  cenl 
regarded  as  necessary  for  fertility. 

Southern  California. — The  soils  of  the  valleys  of  Southern 
California  represented  by  the  composite  of  twenty-five  columns 
have  about  the  same  humus  content  in  the  first  foot  and  in  the 
upper  three  feet  as  was  found  in  similar  parts  of  the  columns 
from  the  Sacramento  Valley  and  the  foothills,  but  are  far  behind 
those  of  the  Coast  Range  valleys.  The  humus  is  well  distributed 
downward  to  twelve  feet,  and  as  with  the  Sacramento  soils 
affords  an  excellent  and  large  feeding  area  for  plant  roots ;  every 
encouragement  should  be  given  crops  to  take  advantage  of  this 
by  sending  their  roots  deep  into  this  fertile  soil  mass.  The  upper 
three  feet  contains  a  little  less  than  one-half  of  the  total  humus. 

The  humus  of  the  first  foot  is  too  low  for  the  maintenance  of 
good  physical  condition  and  careful  attention  should,  as  a  rule, 
be  given  to  the  turning  under  of  green  crops  and  the  humification 
of  the  same. 

The  humus  in  the  upper  three  feet  contains  5.74  per  cent  of 
nitrogen,  but  this  gives  only  the  small  amount  of  0.03  per  cent  to 
the  soil:  this  is  equivalent  to  about  1200  pounds  per  acre-foot, 
which  under  the  influence  of  bacteria  gradually  becomes  available 
for  plants. 

"Desert"  Plains. — The  desert  lands  represented  by  a  com- 
posite of  five  columns  from  the  valleys  of  Imperial,  Coachella, 
Owens  River,  and  Mojave  River  are  very  low  in  humus  in  their 
upper  several  feet,  as  is  to  be  expected  from  the  meagerness  of 
the  natural  humus-forming  vegetation.  One-half  of  the  humus  is 
held  in  the  upper  five  feet  instead  of  in  three,  as  is  the  case  with 
other  regions.  The  presence  of  so  much  humus  in  the  twelfth 
foot  is  a  matter  of  some  surprise,  for  the  lands  seem  usually 
quite  deficient  in  natural  moisture  other  than  hygroscopic  for 
hundreds  of  feet  in  depth.  The  amount  of  humus  in  the  twelfth 
foot  is  one-half  that  of  the  first  foot.  The  humus  of  the  upper 
three  feet  contains  but  4.97  per  cent  of  nitrogen,  which  gives  but 
0.01  per  cent  of  organic  nitrogen  in  the  soil :  this  is  equivalent 
to  about  four  hundred  pounds  per  acre-foot,  which  is  very  little. 

Lava-bed  Region. — The  valley  lands  of  the  Lava-bed  region 


258  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

of  the  northeastern  part  of  the  state  have  in  the  composite  of 
eight  columns  a  high  percentage  of  humus,  not  only  in  the  first 
foot  but  in  the  second.  This  is  natural  as  the  soils  are  moist 
from  underlying  water  and  there  is  a  strong  vegetation  whose 
roots  penetrate  deeply.  The  total  sum  of  humus  percentages  in 
the  twelve  feet  is  4.25  per  cent,  the  upper  three  feet  holding  more 
than  one-half  of  it.  The  humus  is  poorer  in  nitrogen  than  in  any 
of  the  regions  except  the  desert,  the  average  in  the  upper  three 
feet  being  3.79  per  cent,  or  0.05  per  cent  in  the  soil. 

Tule  Marshes. — The  tule  marshes  near  Stockton  and  Klamath 
and  the  Pomona  cienega  have  extremely  high  humus  percentages 
in  each  of  the  four  upper  feet,  and  the  humus  is  also  quite  high 
through  the  column  of  seven  feet,  all  derived  from  the  large 
amount  of  decaying  tule  roots.  The  humus-nitrogen  of  the 
upper  three  feet  is,  however,  only  5.75  per  cent  in  the  humus  or 
0.4-4  per  cent  in  the  soil;  the  latter  is  much  higher  than  found 
in  any  of  the  columns. 


Nitrogen  in  the  Humus  and  in  the  Soil 

Nitrogen  exists  in  the  soil  partly  in  the  free  state  in  the  air 
that  permeates  the  soil;  partly  in  the  vegetable  and  animal 
material  that  has  not  undergone  humification ;  partly  in  the 
humified  vegetable  and  animal  matter;  and  partly  as  nitrates 
soluble  in  water,  and  hence  very  variable  in  amount  from  day 
to  day  and  liable  to  be  lost  by  drainage.  That  the  unhmufied 
material  in  the  soil  does  not  yield  its  nitrogen  to  the  plants  until 
after  complete  humification  has  been  shown  by  the  experiments 
of  Professor  Hilgard,  whose  conclusions  are  as  follows : 

"It  thus  appears  that  although  the  nitrogen  of  the  un- 
humified  organic  matter  constituted  about  40  per  cent  of  the 
total  in  the  original  soil,  it  would  during  the  entire  year  have 
contributed  only  to  an  insignificant  extent  to  the  available 
nitrate  supply;  while  the  fully  humified  'matiere  noire'  con- 
tributed fourteen  times  as  much.  During  the  growing-season  of 
four  or  five  months  the  unhumified  organic  matter  would  have 
yielded  practically  nothing  to  the  crop."" 


»Soila  (Macmillan  &  Co.,  1906),  p.  3G0. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         259 

The  humus  itself  then  is  the  most  reliable  source  of  nitrogen, 
keeping  it  in  reserve  to  be  given  to  the  roots  of  plants  by  degrees 
by  ammonifying  and  nitrifying  bacteria  and  at  the  time  when 
most  needed,  namely,  in  the  growing  season.  The  fertilizing 
value  of  humus  depends,  as  has  already  been  remarked,  upon 
the  amount  of  nitrogen  that  it  contains  and  which  may  be 
changed  to  ammonia  and  nitrates  through  the  agency  of  bacteria 
and  given  to  the  soil  and  plant.  The  nitrogen  content  naturally 
varies  according  to  the  nature  of  the  materials  from  which  the 
humus  was  formed  and  to  any  diminution  that  may  have  occurred 
from  bacterial  action  or  other  causes,  and  we  therefore  find 
great  differences  in  one  and  the  same  column  of  soil.  Sometimes 
the  difference  is  very  great  between  one  foot  and  the  next,  for 
which  it  is  difficult  to  account. 

Nitrogen  in  Humus. — More  than  one  thousand  of  these 
nitrogen  determinations  in  the  humus  of  the  soil  columns  have 
been  made  and  the  results  were  found  to.  vary  from  1  per  cent 
to  24  per  cent,  but  the  greater  number  were  from  4  per  cent  to 
6  per  cent. 

The  highest  percentage  of  nitrogen  in  humus  was  24.10  per 
cent,  found  in  the  eighth  foot  of  the  Berkeley  adobe  column,  and 
in  this  were  three  other  levels  with  more  than  10  per  cent,  all 
of  which  were  below  the  sixth  foot.  The  column  from  Kenwood, 
Sonoma  County,  had  in  its  sixth  foot  23.2  per  cent,  while  two 
others  of  its  series  had  above  10  per  cent.  The  sixth  foot  of 
the  Santa  Paula  soil  had  20.5  per  cent  and  in  the  fifth  and 
ninth  foot  there  was  more  than  10  per  cent.  The  humus  of  the 
entire  soil  column  from  Fullerton,  from  the  place  of  Dr.  S.  S. 
Twombly,  has  the  credit  of  being  richer  in  nitrogen  than  any 
soil  thus  far  examined,  the  fifth  foot  having  20.5  per  cent,  the 
eighth  and  tenth  having  more  than  19  per  cent  each,  the  third 
18.4,  and  the  others  above  10  per  cent,  excepting  the  second 
foot  which  has  7.8  per  cent;  the  general  average  of  the  column 
is  15  per  cent.  The  amount  of  humus  is,  however,  quite  small 
throughout  the  column,  and  hence  the  amount  of  humus-nitrogen 
given  to  the  soil  is  but  0.05  per  cent.  The  humus  of  the 
Kearney  Park  soil  is  another  notable  example  of  rather  high 
percentages  of  nitrogen,  as  in  each  of  the  seven  feet  below  the 


260  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

upper  foot  there  is  more  than  10  per  cent;  but  here  again  the 
amount  of  humus  is  small.  The  Chico  column  should  also  be 
mentioned,  as  from  the  fifth  to  the  twelfth  the  humus  of  each 
foot  contains  from  10  to  14  per  cent  of  nitrogen,  except  the  ninth 
which  has  9.5  per  cent. 

In  the  one  thousand  determinations  of  nitrogen  there  were 
but  sixty-four  instances,  or  about  6.4  per  cent,  where  the  humus 
contained  more  than  10  per  cent  of  nitrogen :  fourteen  of  these 
have  from  15  to  20  per  cent  and  six  have  above  20  per  cent.  The 
general  average  of  all,  including  the  marshes,  is  5.92  per  cent 
for  the  first  foot,  5.60  per  cent  for  the  upper  three  feet  and 
5.57  per  cent  for  the  entire  depth  of  twelve  feet. 

The  humus  of  the  surface  foot  of  the  composite  of  Southern 
California  soils  is  richer  in  nitrogen  than  that  of  any  of  the 
other  regions,  though  nearly  equalled  by  that  of  the  tule  marshes. 
That  of  the  lava-bed  valleys  is  poorer  in  nitrogen  than  any. 

When  we  consider  the  upper  three  feet  of  the  composite 
columns  we  find  that  the  humus  of  the  San  Joaquin  Valley  is 
much  the  richest  and  that  of  the  lava  beds  again  the  poorest. 
Four  of  the  eight  columns  fall  below  the  general  average  for  the 
state.  The  same  is  true  for  the  averages  of  the  twelve  foot 
columns. 

The  differences  in  the  percentages  of  nitrogen  in  the  humus 
of  the  upper  three  feet  and  of  the  total  column  are  not  very 
great,  especially  in  the  valleys  of  the  Coast  Range,  where  the  two 
are  very  nearly  the  same;  in  the  Sacramento  Valley,  Southern 
California  lava  beds  and  the  desert  plains  the  average  in  the 
column  is  considerably  less. 

Organic  Nitrogen  in  the  Soils. — It  is  well  to  remark  here  that 
0.10  per  cent  of  humus-nitrogen  in  the  upper  foot  of  a  humid 
soil  is  regarded  as  an  ample  supply  for  fertility,  while  in  the 
arid  region  with  its  deeper  soil,  deeper  humus  and  deeper  root 
penetration,  one-half  of  that  amount,  or  0.05  per  cent  in  each 
of  the  three  upper  feet  is  considered  sufficient  for  many  years, 
because  the  roots  are  in  a  deeper  feeding  area  than  in  the  humid 
region,  and  bacterial  activity  is  greater  and  deeper.  This  per- 
centage would  mean  2000  pounds  of  nitrogen  per  acre  in  each 
fool. 


1914]       Loughridge:  Humus  and  Nitro gen  in  California  Soil  Columns         261 

The  marsh  or  tule  soils  of  the  state  have  very  high  amounts 
of  nitrogen,  as  shown  in  the  Stockton  tule  (0.83  per  cent), 
Klamath  tule  (0.34  per  cent),  and  the  Pomona  cienega  (0.25  per 
cent).  The  nitrogen  is,  however,  less  available  than  that  of 
the  dry  uplands,  and  a  comparison  cannot  be  made.  The  two 
soils  from  the  Arroyo  Grande  Valley,  including  the  Routzahn 
seed-farm,  are  highest  among  the  other  soil  columns  with  their 
0.16  per  cent  of  nitrogen  each ;  the  next  highest  are  Gilroy  with 
0.15  per  cent ;  Berkeley  and  Farmington  each  with  0.14  per  cent ; 
Burpee  seed-farm  of  Lompoc,  Vaca  Valley,  and  Kenwood  each 
with  0.13  per  cent;  and  El  Verano,  Santa  Maria,  Chico,  Yount- 
ville,  and  Chino  each  with  0.11  per  cent.  Newcastle  soil  has 
0.10  per  cent,  while  all  others  have  less  than  that.  The  results 
show  most  certainly  that  the  lands  represented  by  these  fourteen 
soils  should  not  need  fertilization  with  nitrate  fertilizers  for 
many  years. 

Nine  of  the  soils  have  but  0.01  per  cent  of  humus-nitrogen  in 
the  first  foot,  seven  have  but  0.02;  forty-six  or  nearly  half  of 
the  columns  have  less  than  0.05  per  cent,  and  hence  are  much 
below  the  desirable  percentage  of  nitrogen.  The  average  of  the 
first  foot  of  all  of  the  columns,  except  the  marshes,  is  about 
0.05  per  cent. 

Some  of  the  upland  soils  are  quite  rich  in  organic  nitrogen  in 
the  upper  three  feet,  the  true  soil  of  the  arid  region.  The  adobe 
of  Berkeley  is  the  richest  with  its  0.13  per  cent  or  approximately 
15,000  pounds  per  acre  in  a  depth  of  three  feet.  Eight  columns 
have  averages  of  0.10  and  upward,  viz.,  the  two  Arroyo  Grande 
soils,  Gilroy,  Chico,  Farmington,  Kenwood,  Newcastle,  and 
Cottonwood.  Thirty-one  columns  have  averages  of  from  0.06 
to  0.10  per  cent,  all  others  being  below  this  amount.  In  other 
words  we  find  that  more  than  half  of  the  columns  have  less  than 
the  0.05  per  cent  of  organic  nitrogen  in  their  upper  three  feet 
which  is  considered  necessary  for  fertility.  Many  have  but  little 
more  than  traces  of  nitrogen. 

In  the  entire  column  of  twelve  feet  we  find  that  there  are 
eleven  upland  localities  that  have  averages  of  as  much  as  0.05  per 
cent,  and  among  these  Berkeley  and  Arroyo  Grande  columns 
stand  highest  with  averages  of  0.08  per  cent  or  approximately 


262  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

38,000  pounds  of  organic  nitrogen  distributed  through  the  depth 
of  twelve  feet. 

HUMUS  IN  SOILS  OF  DIFFERENT  TEXTURE 

We  have  grouped  together  in  the  following  table  the  humus 
percentages  of  soil  columns  having  similar  texture  and  similar 
characters  in  order  to  ascertain  whether  these  have  any  influence 
upon  the  amounts  of  humus.  For  the  textural  classification  of 
the  soils  we  have  used  that  of  Professor  Hilgard,10  the  basis  of 
which  is  the  percentage  of  clay  in  the  soil.  Thus  soils  with 
3  per  cent  and  less  are  classed  as  very  sandy,  those  with  from 
3  to  10  per  cent  of  clay  as  sandy,  with  from  10  to  15  per  cent 
as  sandy  loams,  with  from  15  to  25  per  cent  as  clay  loams,  with 
25  to  35  per  cent  of  clay  as  clay  soils,  and  those  with  more  than 
35  per  cent  of  clay  are  classed  as  heavy  clays,  among  which  are 
the  adobes  of  California  and  other  states  of  the  arid  west. 


Table  46. — Average  of  Humus  in  Lands  of  Different  Texture  at 
Various  Depths 

Very  sandy  Sandy  Sandy  loam  Clay  loam  Clay        Heavy  adobe 

1-3%  clay  3-10%  clay  10-15%  clay  15-25%  clay  25-35%  clay      -35%  clay 

9  columns  15  columns  21  columns  23  columns  8  columns  10  columns 

Per  cent  Per  cent  Per  cent  Per  cent  Per  cent  Per  cent 

1  ft 62  .81  .97  1.33  2.03  1.56 

2  ft 50  .62  .77  .98  1.25  1.23 

3  ft 37  .43  .55  .73  1.11  .95 

4  ft 31  .35  .43  .63  .89  .61 

5  ft 29  .35  .37  .48  .68  .43 

6  ft 21  .35  .31  .41  .52  .37 

7  ft 20  .31  .30  .34  .53  .28 

8  ft 14  .26  .24  .28  .40  .21 

Oft 12  .20  .19  .24  .37  .17 

10  ft 07  .19  .20  .22  .29  .17 

lift 04  .15  .14  .20  .19  .14 

12  ft 03  .16  .12  .19  .25  .13 

Sum  of  per  cents: 

Upper  3  feet....     1.49  '  1.86  2.29  3.04  4.39  3.74 

[Jpper  6  feet....     2.30  2.91  3.40  4.56  6.48  5.15 

Lower  6  feet 60  1.27  1.19  1.47  2.03  1.10 

Entire  column..     2.90  4.18  4.59  6.03  8.51  6.25 

'"Soils  (Maemillao  &  Co.),  p.  84. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         263 

It  is  interesting  to  note  in  each  of  these  composite  columns 
of  soils  the  quite  regular  decrease  in  the  amount  of  humus  from 
the  surface  to  the  twelfth  foot,  thus  indicating  that  in  each  the 
humus  has  been  derived  from  the  decay  of  plant  roots  rather 
than  from  vegetable  material  deposited  during  the  building-up 
of  the  soil  strata.  It  also  gives  testimony  to  the  deep  rooting  of 
plants  of  all  kinds,  notably  grasses  and  weeds  during  the  ages 
that  have  passed. 

Another  interesting  point  is  the  regular  increase  in  the  humus 
percentages  from  a  minimum  in  the  very  sandy  to  the  maximum 
in  the  clay  and  then  a  decrease  in  the  adobe  clays,  not  only  in 
the  surface  foot  of  these  composite  soil  columns  but  also  in  each 
succeeding  foot  down  to  the  twelfth,  the  only  exceptions  being 
slight  ones  in  the  sandy  loam  series  which  are  a  little  less  than 
in  the  sandy. 

It  is  clearly  evident,  then,  that  as  a  rule  the  clay  soils,  except- 
ing the  adobe  clays,  of  the  state  have  a  higher  percentage  of 
humus  than  any  other  class;  and  that  the  humus  content  in 
the  series  increases  with  the  increase  in  clay  up  to  a  certain 
point  when  there  is  a  decrease. 

The  tables  show  that  the  lower  half  of  the  heavy  adobe  clays 
has  a  smaller  percentage  of  humus  than  any  other  class  except 
the  very  sandy ;  the  inference  being  that  the  close,  compact,  heavy 
clay  strata  have  prevented  the  extension  of  plant  root  systems 
to  the  lighter  soils. 

It  will  also  be  noted  that  one-half  of  the  total  humus  in  each 
of  the  composite  columns  is  held  in  the  upper  three  feet,  with 
the  exception  of  the  sandy,  in  which  it  is  held  in  four  feet. 

Comparison  of  Individual  Heavy  Black  Adobe  Clay  Soils 

The  heavy  clay  soils  known  as  adobe  clay  and  containing  from 
35  per  cent  of  clay  upward  to  as  high  as  62  per  cent  are  found 
in  isolated  areas  throughout  the  state,  the  largest  being  in  the 
region  of  Stockton.  They  form  a  distinct  class  possessing 
peculiar  physical  properties.  The  surface  soil  is  usually  black 
to  a  depth  of  three  or  more  feet,  changing  to  a  lighter  color 
below  and  generally  resistant  to  the  easy  movement  of  water, 
plant  roots,  and  tillage  implements,  though  the  roots  of  ordinary 


264  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

weeds  have  been  followed  to  the  depth  of  eleven  feet  below  the 
surface,  and  alfalfa  roots  have  been  observed  at  a  depth  of 
twenty-six  feet  in  the  adobe  of  Berkeley.  It  is  extremely  plastic 
when  wet,  but  when  dry  it  absorbs  water  with  extreme  slowness. 
Because  of  the  black  color  it  was  supposed  that  the  humus  content 
would  be  found  to  be  quite  high  in  all  localities,  but  the  dis- 
appointment following  the  examination  of  many  columns  has 
induced  us  to  present  them  in  a  table  for  comparison ;  the  figures 
for  humus  and  for  amount  of  clay  are  taken  from  the  report  on 
the  several  agricultural  regions  already  given.  The  ''adobe" 
soils  in  which  there  is  less  than  35  per  cent  of  clay  are  omitted 
from  the  table. 

Table  47.— Percentage  of  Humus  in  Columns  of  Black  Adobe  Clay 


►  epth 

Santa 
Clara 

Berke- 
ley 

East  of 
Willows 

Walnut 
Creek 

San 
Ramon 

South  of 
Yuba 
City 

Stock- 
ton 

Kings 
City 

South  of 
Dixon 

West  of 
Tracy 

Biggs 

59% 
clay 

44% 
clay 

48% 
clay 

35% 
clay 

45% 
clay 

39% 
clay 

57% 
clay 

35% 
clay 

62% 
clay 

40% 
clay 

50% 
clay 

*  1ft. 

4.43 

2.13 

1.72 

1.42 

1.23 

1.20 

1.16 

1.15 

.86 

.82 

.66 

2  ft. 

3.66 

2.04 

1.16 

1.44 

1.28 

.21 

.76 

.90 

.62 

.70 

.49 

3  ft. 

2.80 

1.84 

.94 

1.16 

1.08 

.18 

.50 

.61 

.34 

.30 

.40 

4  ft. 

.61 

1.90 

.62 

1.12 

.84 

.18 

.22 

.25 

.28 

.12 

.17 

5  ft. 

.27 

.95 

.36 

1.08 

.81 

.11 

.22 

.52 

.30 

.19 

.06 

6  ft. 

.20 

1.06 

.26 

.72 

.75 

.10 

.41 

.41 

.30 

.09 

.06 

7  ft. 

.62 

.48 

.22 

.60 

.29 

.08 

.11 

.43 

.30 

.09 

8  ft. 

.23 

.37 

.20 

.60 

.20 

.12 

.09 

.37 

.26 

.00 

.06 

9  ft. 

.30 

.36 

.14 

.42 

.14 

.12 

.08 

.33 

.07 

.00 

.05 

10  ft. 

.13 

.36 

.22 

.52 

.12 

.12 

.07 

.11 

.07 

.00 

.04 

lift. 

.45 

.20 

.36 

.09 

.13 

.09 

.09 

.00 

.06 

12  ft. 

.49 

.16 

.26 

.07 

.11 

.09 

.00 

.09 

It  is  a  matter  of  much  surprise  that  the  heavy  black  clay  or 
adobe  soils  of  the  state  should,  generally,  have  so  little  of  humus 
in  the  upper  three  feet  and  especially  in  the  surface  soil.  Only 
two  of  the  eleven  columns  chosen  as  typical  of  the  various  black 
clay  regions  have  as  much  as  2  per  cent  in  the  upper  foot.  The 
black  adobe  of  the  Sacramento  and  San  Joaquin  valleys  have  far 
less  humus  than  was  found  in  those  of  the  Coast  Range.  It  is 
also  a  surprising  fact,  well  shown  in  these  soils,  that  a  black 
soil  docs  not  always  owe  its  color  to  the  humus  that  it  contains, 
for  all  of  those  given  in  the  table  are  very  black  and  yet  have 
but    little    humus;    this    is   especially   noticeable   in   those   from 


1914]      Loughridge:  Humus  and  Nitrogen  in  California  8oU  Col am  nt         265 

Tracy.  Biggs,  and  south  of  Dixon,  which  have  less  than  1  per 
cent.  A  very  striking  example  of  this  was  found  in  a  sample 
of  adobe  soil  sent  for  examination  some  time  ago  from  near  the 

hills  in  the  Santa  Clara  Valley,  which  although  almost  jet  black 
had  but  a  trace  of  humus. 

It  is  further  interesting  to  note  that  in  the  Berkeley  and 
Walnut  Creek  columns  there  is  more  than  1  per  cent  of  humus 
in  each  of  the  upper  six  and  five  feet  below  the  surface  respec- 
tively; in  each  of  the  upper  three  feet  of  the  Santa  Clara  and 
San  Ramon  columns  and  in  the  upper  two  feet  of  the  Willows 
column.  In  the  Dixon.  Tracy,  and  Biggs  columns  there  is  less 
than  1  per  cent  in  the  first  foot. 

In  the  fourth  foot  of  the  Santa  Clara,  seventh  foot  of  the 
Berkeley,  and  third  foot  of  the  Yuba  City  there  are  very  sharp 
drops  in  the  percentages,  and  this  is  seen  also  in  the  lighter  color 
of  the  respective  columns  at  those  depths.  These  indicate  that 
the  main  root  systems  of  the  plants  were  confined  to  the  upper 
part  of  these  soils,  while  in  other  columns  there  was  less  of  root 
mass  and  a  greater  downward  development.  In  all  except  where 
ground  water  was  found  above  the  twelfth  foot,  the  humus 
clearly  could  be  found  at  greater  depth,  especially  in  the  Berkeley 
column,  which  had  0.-49  per  cent  in  the  twelfth  foot. 

The  Santa  Clara  soil  has  in  its  first  foot  the  highest  per- 
centage of  humus  of  any  soil  of  the  state  thus  far  examined, 
excepting  the  tule  marshes ;  the  same  is  true  if  we  compare  the 
average  of  the  three  upper  feet  and  also  that  of  the  upper  six 
feet,  which  are  respectively  3.62  and  1.99  per  cent.  The  general 
average  of  humus  in  the  first  foot  of  the  eleven  columns  is  1.61, 
for  the  second  1.20.  and  for  the  third  foot  only  0.92  per  cent. 

Relation  of  Humus  Percentage  to  Color  and  other 

Soil  Characters 

There  are  types  of  land  having  other  than  textural  charac- 
teristics concerning  whose  relation  to  humus  content  some  ques- 
tion may  arise,  and  we  have  segregated  some  of  the  more 
important  of  these  in  the  following  table.  They  refer  to  the 
uplands  and  lowlands,  the  several  color  characters  and  to  strong 


266  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

alkali  lands.  We  have  omitted  the  tule  marsh  lands  from  the 
composite  of  lowlands,  and  the  strong  alkali  lands  and  the  desert 
lands  from  the  composite  of  uplands. 

Table  48. — Average  Humus  in  Soils  of  Different  Character  and  Color 


Stream 
alluvial 

Non-alkali 
uplands 

Black 
lands 

Gray 
lands 

Red 

lands 

Alkali 
land 

5  columns 

73  columns 

17  columns      16  columns 

10  columns 

4  columns 

1  ft.... 

1.41 
1.09 

1.18 
.91 

1.19 
.45 

.94 
.69 

.64 
.42 

.30 

2  ft.... 

.26 

3  ft.... 

.84 
.76 

.65 
.37 

.38 
.26 

.57 
.47 

.28 
.24 

.23 

4  ft... 

.18 

5  ft.... 

.68 
.56 

.42 
.36 

.22 
.21 

.44 

.40 

.24 

.17 

.16 

6  ft... 

.08 

7  ft.... 

.52 

.35 

.15 

.37 

.12 

.08 

8  ft.... 

.41 

.27 

.12 

.30 

.10 

.06 

9  ft.... 

.34                  .25                  .11 
.24                  .24                  .09 
.26                  .23                  .05 
.23                  .23                  .08 

Combination  of  Upper  and 

.31                 .11 
.28                  .11 
.25                  .12 
.22                  .18 

Lower  Portions 

.04 

10  ft,... 

.04 

11  ft.... 

.04 

12  ft.... 

.03 

Sum  of 

'  per  cents 

Upper 

3  feet.... 

3.34 

2.74 

2.02 

2.20 

1.34 

.79 

Upper 

6  feet.... 

5.34 

3.89 

2.71 

3.51 

1.99 

1.21 

Lower  6  feet.... 

2.00 

1.57 

.60 

1.73 

.74 

.29 

Total  12  feet.... 

7.34 

5.46 

3.31 

5.24 

2.73 

1.50 

Average  per  ft. 

.61 

.45 

.28 

.44 

.23 

.12 

The  table  shows  the  interesting  and  unexpected  fact  that  in 
their  general  averages  the  alluvial  lands  that  border  the  streams 
are  but  little  richer  in  humus  than  the  uplands,  either  in  the 
surface  foot  or  at  the  several  levels  to  the  twelfth  foot.  In  the 
fourth  foot  the  difference  is  0.39  per  cent,  but  in  every  other 
level  it  is  less  than  that.  In  the  upper  three  feet  the  difference 
is  0.60  per  cent,  in  the  upper  six  feet  1.45,  and  for  the  entire 
column  it  is  only  1.88  per  cent  in  favor  of  the  alluvial  lands. 
There  are,  of  course,  throughout  the  state  instances  of  high 
percentages  in  single  soils  of  both  the  alluvial  and  upland  classes, 
and  but  for  these  the  general  averages  would  be  much  lower. 

The  close  agreement  in  humus  percentages  of  the  uplands  and 
alluvial  lands,  and  the  gradual  and  quite  uniform  diminution  of 
the   same   downward    plainly   indicates   that   the   source   of   the 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         267 

humus  in  both  classes  is  in  the  decay  and  humification  of  plants 
whose  roots  had  penetrated  to  depths  of  many  feet. 

The  small  differences  throughout  the  composite  columns  would 
also  show  that  the  alluvial  lands  and  the  deltas  possess  no  material 
advantage,  except  perhaps  in  moisture  conditions,  over  the  higher 
lands  which  are  of  good  depth  and  free  from  hardpan. 

Relation  of  Humus  to  Soil  Color. — It  has  already  been  pointed 
out  that  a  black  color  does  not  necessarily  mean  the  presence  of 
a  high  percentage  of  humus,  and  this  is  again  emphasized  in  the 
composite  columns  of  many  soils  of  three  colors  taken  from  the 
main  agricultural  regions  of  the  state.  In  these  the  surface  foot 
of  the  black  has  but  little  more  humus  than  that  of  the  gray 
soil  (1.19  and  0.94  per  cent  respectively).  But  still  more  sur- 
prising is  the  fact  that,  although  the  upper  three  feet  of  the 
black  lands  are  almost  invariably  very  dark  and  even  black, 
they  contain  less  humus  than  the  upper  three  feet  of  the  gray 
sandy  lands;  and  that  throughout  the  entire  composite  columns 
the  percentage  of  humus  is  greater  in  the  gray  than  in  the  black 
soils  with  the  exception  of  the  first  foot.  There  are,  of  course, 
black  clay  lands  of  Santa  Clara,  Arroyo  Grande,  and  other 
localities  which  have  high  percentages,  but  these  are  offset  by 
those  with  very  small  amounts. 

The  composite  of  eleven  red  lands  embracing  mesa  and  hill 
lands  and  the  more  level  lands  on  the  eastern  side  of  the  great 
valley  contains  less  humus  than  either  the  black  or  the  gray, 
except  in  the  lower  six  feet. 

The  gray  lands  of  the  state  seem  therefore  to  have  greatly  the 
advantage  over  both  the  black  and  red  classes  in  larger  humus 
content  and  in  its  better  distribution  throughout  the  depth  of 
twelve  feet. 

Humus  in  Strong  Alkali  Soils. — This  column  is  a  composite 
of  four  alkali  soils  from  the  San  Joaquin  Valley,  including  the 
Tulare  Lake  bed,  and  shows  a  deficiency  in  humus  throughout. 
Alkali  salts  are  usually  held  in  the  upper  four  feet  of  these 
valley  soils  and  it  is  there  where  they  would  prevent  the  growth 
of  vegetation  with  accompanying  root  systems  whose  decay  would 
result  in  the  production  of  humus.  Hence  we  find  but  little  more 
than  mere  traces  of  humus  below  the  fifth  foot. 


268  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

HUMIC  PHOSPHORIC  ACID  IN  SOILS 

While  one  of  the  chief  values  of  humus  lies  in  its  content  of 
nitrogen  which  is  made  available  to  plants  by  bacterial  action, 
the  mineral  elements  potash  and  phosphoric  acid  held  by  it  are 
also  of  value  to  plants  as  fertilizers  and  are  probably  immedi- 
ately available.  The  amount  of  phosphoric  acid  is  especially 
quite  large,  as  is  shown  by  an  analysis  of  the  ash  from  humus 
of  a  productive  prairie  soil  of  Minnesota  made  by  Professor 
Snyder.11 


Table  49. — Analysis  of  the  Ash  of  Humus 

Per  cent 

Ash  (precipitated  humus)  12.24 

Composition  of  the  Ash 

Silica    61.97 

Potash    7.20 

Soda    8.13 

Lime   0.09 

Magnesia   0.36 

Ferric  oxid 3.12 

Alumina  3.48 

Phosphoric  acid  12.37 

Sulfuric  acid  0.98 

Carbonic  acid  1.64 


Early  in  the  investigation  of  the  humus  in  these  soil  columns, 
we  made  examinations  of  the  ash  of  the  humus  of  a  few  of  the 
soil  columns  to  their  full  depth  to  ascertain  how  much,  if  any, 
phosphoric  acid  was  present  in  an  organic  form  combined  with 
the  humus  below  the  upper  few  feet.  The  difficulty  of  securing 
a  humus  solution  free  from  suspended  clay  makes  the  results 
given  in  the  following  table  only  approximately  correct,  though 
sufficiently  so  to  be  of  special  interest  in  showing  that  phosphoric 
acid  docs  accompany  the  humus  in  all  soils  to  depths  of  many 
feet,  nnd  being  thus  distributed  downward  throughout  the  soil 
mass  is  ;i1  the  command  of  roots  as  they  reach  to  water. 


u  Chemistry  of  Soils  and  Fertilizers. 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         269 


Table  50.. — Percentage  of  Humus  and  Humic  Phosphoric  Acid  in  Several 
of  the  Soil  Columns 


i  ft 

2  ft 

3  ft 

4  ft 

5  ft 

6  ft 

7  ft 

8  ft 

9  ft 

10  ft 

11  ft 

12  ft 

Total  av 
1st  ft. 

6th  ft. 

12th  ft. 


Orchard 
Yuba  City 
Clay  loam 

Orchard 

Chico 

Alluvial 

Grain  field        Grain  field 
Stockton            Modesto 
Adobe  clay           Sandy 

Hop  field 

Russian 

River 

Alluvial 

Seed  farm 

Santa 

Clara 
Adobe  clay 

Orchard 

Santa 

Paula 

Clay  loam 

CO 

0 

a 

'u 
ft  3 

Ph 

CO 

0 

a 

0 

w 

u 

'u 

.§3 

a  « 
§* 

Ph 

co 

0 

a 

0 

w 

o 

a« 

co  c8 

O 
XS 
Ph 

CO 

a 
0 

a 

'u 

fto 

CO* 

A 
Ph 

3 

a 
B 

o 

"u 

p.  u 

CO     CS 

O 

A 

0 

a 

a  o 
cc  ce 
c 

Ph 

CO 

Ph 

a  5 

pm 

1.27 

.05 

1.84 

.05 

1.16 

.05 

37 

.01 

1.30 

.07 

4.43 

.07 

1.23 

.07 

1.08 

.04 

1.18 

.04 

.76 

.03 

.27 

.01 

1.24 

.09 

3.66 

.04 

1.36 

.07 

.45 

.02 

1.16 

.03 

.50 

.02 

.19 

.01 

1.20 

.08 

2.80 

.02 

.52 

.04 

.39 

.02 

.88 

.02 

.22 

.02 

.18 

.02 

1.18 

.06 

.61 

.06 

.57 

.04 

.67 

.02 

.58 

.01 

.22 

.04 

.17 

.01 

.75 

.03 

.27 

.05 

.54 

.04 

.48 

.03 

.42 

.02 

.18 

.03 

.16 

.01 

.61 

.02 

.20 

.05 

.48 

.02 

.22 

.03 

.40 

.01 

.11 

.02 

.17 

.01 

.48 

.03 

.62 

.09 

.54 

.04 

.16 

.02 

.36 

.01 

.09 

.01 

.78 

.07 

.23 

.05 

.45 

.05 

.12 

.02 

.38 

.02 

.08 

.02 

.... 

.64 

.07 

.30 

.08 

.36 

.05 

.11 

.01 

.46 

.02 

.07 

.01 

.52 

.06 

.51 

.04 

.12 

.01 

.32 

.02 

.09 

.02 

.54 

.04 

.60 

.03 

.11 

.01 

.52 

.02 

.11 

.02 

.22 

.04 

.52 

.03 

ible  ph 

osphoric  acia 

in  soil : 

.18 

.09 

.06 

.11 

.18 

.12 

.12 

.11 

.10 

.11 

.11 

.23 

.10 

.19 

.09 

.13 

.23 

.13 

.26 

.12 

.22 

It  will  be  seen  from  this  table  that  the  highest  amounts 
of  phosphoric  acid  in  organic  combinations  occur  in  the  upper 
two  feet  of  each  column  with  the  exception  of  the  Russian  River 
and  the  Santa  Clara,  each  of  which  have  high  percentages  in 
their  lowest  depths,  although  the  amount  of  humus  is  much 
lower  than  in  the  upper  part. 

The  general  average  is  0.05  per  cent  for  each  of  the  two  upper 
feet  of  the  seven  columns,  0.03  per  cent  for  each  of  the  succeed- 
ing eight  feet,  and  0.02  per  cent  for  each  of  the  two  lowest  feet 
of  the  five  columns  whose  depth  reaches  twelve  feet  respectively. 

If  we  estimate  the  percentages  into  pounds  per  acre,  we  find 
that  the  amount  of  this  humic  phosphoric  acid  for  the  column 
is  approximately  as  follows: 


270  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Surface  foot  Upper  3  feet  Entire  column 

Yuba  City,  Sutter  County  2,000  lbs.  4,800  lbs.  11,200  lbs. 

Chico,  Butte  County 2,000  lbs.  4,800  lbs.  10,800  lbs. 

Stockton,  San  Joaquin  County  2,000  lbs.  3,600  lbs.  11,600  lbs. 

Russian  Eiver,  Sonoma  County  2,800  lbs.  9,600  lbs.  26,400  lbs. 

Santa  Paula,  Ventura  County  2,800  lbs.  7,200  lbs.  15,600  lbs. 

Santa  Clara,  Santa  Clara  County....       2,800  lbs.  4,800  lbs.  20,400  lbs. 

Modesto,  Stanislaus  County  400  lbs.  1,200  lbs.  3,200  lbs. 


Even  in  the  upper  foot  of  each  of  the  above  there  is  from 
2000  to  2800  pounds,  with  the  exception  of  that  of  Modesto,  which 
has  only  400  pounds  of  phosphoric  acid  per  acre. 

When  we  consider  the  fact  that  0.05  per  cent  or  2000  pounds 
per  acre  of  available  phosphoric  acid  is  regarded  as  a  sufficient 
amount  for  soil  fertility  for  present  needs,  we  can  readily  see 
that  these  particular  soils,  except  that  from  Modesto,  are  abund- 
antly supplied  with  phosphoric  acid  for  many  years. 

Analyses  of  the  first,  sixth,  and  twelfth  foot  respectively  of 
the  columns  also  show  the  presence  of  large  percentages  of 
available  potash. 


Comparison  of  Arid  and  Humid  Soils 

A  comparison  between  the  soils  of  the  arid  and  humid  regions 
brings  out  the  very  great  advantage  possessed  by  the  former  and 
especially  by  those  of  California  over  the  humid,  as  shown  in  the 
first  part  of  this  bulletin.  But  it  is  especially  marked  in  the 
amount  and  distribution  of  humus  in  the  soils  of  the  respective 
region.12  The  general  average  in  280  soils  of  the  humid  portion 
of  the  United  States  is  2.63  per  cent,  and  if  we  add  to  this  the 
5.26  per  cent  in  eleven  tropical  soils  of  Hawaii  the  average  is 
brought  to  2.73  per  cent,  or  approximately  109,200  pounds  per 
acre  in  a  depth  of  twelve  inches. 

The  average  of  the  331  California  soils  and  forty-four  from 
Idaho,  Arizona,  and  Oregon  is  1.28  per  cent  for  the  surface  foot, 
or  less  than  one-half  that  of  the  humid  region.     For  the  first 


i-  It  lias  been  a  rather  difficult  matter  to  secure  data  on  humus  in  the 
soils  east  of  the  Mississippi  River  for  the  reason  that  in  their  analysis 
some  of  the  chemists  have  failed  to  separate  it  from  the  percentage  of 
aggregate  "organic  matter." 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         271 

foot  of  the   109   soil   columns   including   the   marsh   lands   the 
average  is  1.35  per  cent. 

But  the  depth  of  soil  in  which  most  of  the  plant  roots  are 
held  in  the  arid  region,  and  in  which  the  humus  color  is  most 
pronounced  is  three  feet,  and  taking  this  as  the  true  soil  of 
California  we  find  that  there  is  a  sum  of  3.17  per  cent,  or  an 
average  of  1.06  for  each  foot ;  this  is  equivalent  to  about  127,000 
pounds  per  acre.  To  this  should  be  added  the  percentages  of 
humus  found  at  lower  levels  of  the  soil,  as  shown  in  the  averages 
of  the  109  columns  given  in  the  accompanying  table,  which  would 
bring  the  total  humus  to  233,000  pounds  in  twelve  feet. 


Table  51. — Average  of  Humus  in  Arid  and  Humid  Soils 

Arid  Soils  Humid  Soils 


109  California 
soil  columns 
Per  cent 

r  1.35 

...J      1.04 

.78 


Ft. 

1. 

2.  Soil    

3. 

4.  Subsoil    L       .62 

5.  .45 

6.  .36 

7.  .30 

8.  .26 

9.  .21 

10.  .18 

11.  .14 
12  .14 
Sum  of  per  cents  in  12  ft.  5.83 
Sum  of  per  cents  in  3  ft.  3.17 

Nitrogen  in  humus,  3  ft 5.60 

Nitrogen  in  soil,  3  ft 05 


342  soils 
in  United  States 
Per  cent 

1.28 

? 


291  soils 

in  United  State 

Per  cent 


Soil 


2.73 

? 

00 

00 

00 

00 


The  amount  of  humus  then  in  the  average  of  California  soils 
(three  feet  deep)  is  greater  than  in  those  of  the  humid  region; 
and  for  the  depth  of  twelve  feet  it  is  more  than  twice  as  great. 

The  determinations  of  humus-nitrogen  in  the  soils  of  the 
humid  region  have  been  so  few  and  miscellaneous  that  it  is  not 
advisable  to  deduce  from  them  an  average  to  represent  the  whole 
region. 


272  University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

Arid  California  with  her  deep  soils  of  well  diffused  humus 
and  richness  in  plant  food  thus  possesses  very  great  advantages 
over  the  more  humid  east  where  a  depth  of  six  to  nine  inches 
is  very  generally  accepted  as  that  of  a  true  upland  surface  soil, 
containing  practically  all  of  the  humus  and  marked  by  a  very 
sharp  change  of  the  black  humus  color  to  the  gray  and  yellow 
subsoil  with  its  inappreciable  amount  of  humus.13  In  the  sedi- 
ment lands  of  the  streams  and  some  of  the  black  prairies  the 
humus  is  of  course  found  at  a  greater  depth. 

!    ■    A 

CONCLUSIONS 

1.  The  depth  of  the  soils  of  California  is  indefinite  because  of 
the  presence  of  humus  and  available  plant  food  to  and  beyond 
twelve  feet  below  the  surface.  It  may  be  several  times  twelve 
feet,  being  limited  only  by  ground  water,  country  rock  or  heavy 
beds  of  gravel;  layers  of  hardpan  at  a  depth  of  several  feet 
would  limit  the  depth  for  small  cultures,  but  may  be  broken  up 
with  dynamite  and  the  depth  greatly  increased  for  the  extension 
of  tree  roots.  There  are  in  reality  none  of  those  difficultly 
permeable  clay  subsoils  that  characterize  humid  soils  and  limit 
their  depth  to  but  a  few  feet.  The  sharply  denned  change  of  the 
black  humus  color  to  gray  at  six  or  nine  inches  that  marks  the 
depth  of  humid  soils  is  present  in  some  of  the  heavy  clay  soils 
in  California  at  the  depth  of  three  feet,  but  for  the  most  part 
the  change  in  tint  is  very  gradual  downward  through  many  feet. 
The  upper  three  feet  may,  however,  properly  be  called  the  soil, 
for  in  that  depth  the  greater  part  of  the  feeding  roots  of  plants 
are  found. 

2.  The  soils  of  California  are  richer  in  humus  than  has 
generally  been  supposed;  in  their  depth  of  three  feet  (the  soil 
proper)  they  contain  more  than  in  the  humid  soils,  and  in  the 
entire  columns  of  twelve  feet  or  more  they  have  double  that  of 
the  humid  soils. 


i a  Sec  Eilgard's  Soils,  p.  164,  and  Agricultural  Science,  1892,  p.  263; 
King's  The  Soil,  p.  29;  Hall's  Soils,  p.  45;  Minn.  Agr.  Expt.  Sta.  Bull. 
30,  11,  and  65  contain  analyses  of  121  subsoils,  in  only  sixteen  of  which 
is  humus  reported  though  found  in  all  of  the  corresponding  surface  soils 
which  were  taken  to  depths  of  nine  inches.     (Hull.  30,  p.  164.) 


1914]       Loughridge:  Humus  and  Nitrogen  in  California  Soil  Columns         273 

3.  The  humus  in  California  soils  is  usually  distributed 
through  depths  of  twelve  or  more  feet,  the  highest  percentage 
being  in  the  upper  three  feet  and  diminishing  downward  as 
shown  in  each  of  the  109  soil  columns  taken  from  the  seven 
agricultural  regions;  as  much  as  41  per  cent  was  found  in  the 
fifteenth  foot  of  the  Ft.  Romie  column,  and  0.74  per  cent  in  the 
thirteenth  foot  of  that  of  Davis  and  Hayward ;  water  was  reached 
in  each  case. 

4.  The  surface  soils  of  California  have  an  average  of  1.28  per 
cent  of  humus  as  shown  in  the  analysis  of  several  hundred 
samples  taken  from  the  many  agricultural  regions  of  the  state. 
This  is  not  sufficient  to  maintain  good  tilth  in  the  soil ;  but  as 
supplemented  by  that  of  many  feet  below  often  aifords  a  fair 
supply  of  nitrogen.  The  upper  three  feet  of  soil  proper  has  an 
average  of  1.06  per  cent  per  foot,  or  a  sum  of  3.17  per  cent. 

5.  The  tule  swamps  have  the  highest  percentage  of  humus 
because  of  the  mass  of  decaying  roots  and  other  vegetable  matter, 
while  the  desert  plains  have  the  least. 

6.  Humification  is  retarded  in  close  compact  adobe  clays  and 
the  amount  of  humus  is  less  than  in  lighter  loam  and  sandy  soils. 

7.  The  valleys  of  the  Coast  Range  in  the  western  part  of  the 
state  have  higher  percentages  of  humus  in  their  soils  than  have 
any  of  the  other  agricultural  regions  of  California,  probably 
because  of  the  greater  humidity  of  the  climate  of  that  region 
and  a  denser  vegetation. 

8.  The  humus  of  the  soils  of  this  state  is  very  generally 
derived  from  plant  roots  instead  of  from  accumulations  of 
vegetable  material  at  various  depths  as  the  soil  was  being  built 
up,  thus  showing  that  the  native  vegetation  has  for  ages  been 
deep-rooted. 

9.  The  black  color  of  a  soil  is  not  always  due  to  a  high 
humus  content;  many  black  soils  have  a  smaller  percentage  of 
humus  than  soils  of  a  gray  color.  In  one  instance  a  very  black 
clay  soil  from  the  Santa  Clara  Valley  contained  no  humus,  its 
color  being  due  to  the  presence  of  a  black  rock  powder. 

10.  Humus  contains  nitrogen  in  combination,  the  amount 
depending  largely  on  the  source  of  the  humus.  The  average 
percentage  in  the  humus  of  the  first  foot  of  the  soil  columns  is 


274         University  of  California  Publications  in  Agricultural  Sciences    [Vol.  1 

5.92  per  cent;  that  of  each  of  the  upper  three  feet  is  5.60,  and 
a  little  less  for  the  entire  twelve  feet.  It  varies  from  1  to  20 
per  cent  in  individual  soil  layers. 

11.  The  organic  nitrogen  in  the  soil  derived  from  the  humus 
and  dependent  on  the  amount  of  the  latter,  varies  from  almost 
nothing  in  the  lower  depths  of  the  soil  to  as  much  as  0.13  per 
cent  in  the  upper  three  feet.  The  average  of  the  first  foot  of  the 
soil  columns  is  0.07  per  cent;  for  each  of  the  three  upper  feet, 
the  range  of  most  annual  plant  roots,  it  is  0.05  per  cent.  The 
investigations  of  Professor  Lipman  of  this  station  show  that 
nitrifying  bacteria  are  present  and  active  in  California  soils  to 
depths  of  six  feet  and  ammonifying  bacteria  are  present  through 
a  depth  of  twelve  feet,  thus  making  available  to  plants  the 
nitrogen  content  of  the  humus  to  these  depths. 

12.  Humus  contains  soluble  mineral  plant  food  in  combina- 
tion, the  phosphoric  acid  being  present  in  the  humus  of  Cali- 
fornia soils  to  the  extent  of  from  0.01  per  cent  to  0.08  per  cent 
throughout  the  entire  depth  to  which  humus  reaches,  though 
usually  greatest  in  the  upper  few  feet. 

13.  Humus  is  sometimes  less  in  the  first  foot  than  in  the 
second  because  it  is  gradually  destroyed  by  cultivation  and 
summer  fallowing  of  the  soil,  but  may  be  replaced  and  increased 
by  proper  methods  of  green-manuring,  or  the  turning-under  and 
humification  of  legumes. 

14.  Arid  soils  have  an  immense  advantage  over  those  of  the 
humid  region  of  the  United  States  because  of  this  distribution 
of  humus  and  its  nitrogen,  as  well  as  of  mineral  plant  food, 
through  a  depth  of  many  feet,  as  it  gives  a  greater  depth  of  soil 
and  induces  a  deeper  root  penetration  for  plants  and  trees  into 
a  greater  feeding  area  and  where  there  is  more  moisture.  The 
wonderful  endurance  of  drought  on  the  part  of  California  soils 
is  due  to  this. 

15.  The  practical  value  and  hence  the  commercial  valuation 
of  land  in  California  cannot  be  based  alone  upon  the  nature  of 
the  surface  soil  and  subsoil  as  in  the  humid  region,  but  chiefly 
upon  its  texture  and  depth,  and  upon  the  freedom  with  which 
plant  roots  are  able  to  penetrate  to  many  feet  and  secure  moisture 
and  the  abundant  food  supply  that  exists  at  those  depths  in  all 
of*  California  soils. 


